On June 1st of this year, the European Space Agency’s (ESA) Mars Express spacecraft was able to capture images of an unusual alignment as Mars’ moon Phobos passed in front of Jupiter (seen in background). The images were put together to form this amazing animation.
Mars has two moons – Phobos and Deimos. The origins of these names are a bit gloomy : Phobos, named after a Greek God, means “fear” and Deimos is a figure representing “dread” in Greek mythology. Phobos is the largest of the two, and the closest moon to Mars.
You can see quite clearly that Phobos has an irregular shape – it’s mean radius is only of 11.1 km (6.9 mi). Compare that with our Moon with its mean radius of approximately 1737.5 km (1079 miles). And that seemingly small object behind Phobos is of course Jupiter with a mean radius of (a not so small) 69,911 km (or 43440 miles).
This was a unique opportunity for the Mars Express spacecraft which performed a special maneuver to capture the alignment. At the time these images were taken, there was a distance of 11,389 km (7076 miles) between the spacecraft and Phobos with Jupiter a further 529 million km away.
The Mars Express spacecraft was launched in 2003 and consisted of two parts – the Mars Express orbiter reponsible for the images in the animation above and the Beagle 2 – which was to land on the Martian surface and study the planet’s geochemistry. Sadly the ill-fated Beagle 2 failed to make a safe landing (reminding us that planetary exploration is not easy!). The Mars Express, however, has been collecting valuable data since 2004. In particular, experiments are looking at the atmospheric environment, studying the distribution of water vapour, imaging and analysing the surface composition of Mars and searching for possible ice below the planet’s surface.
The science return and flexibility of the Mars Express has earned it significant mission extensions – in fact it was initially planned to have a mission length of one Martian year (that’s 687 days for we earthlings). It is now expected to continue its operations until December 2012. Find out more about the mission at ESA’s site http://www.esa.int/SPECIALS/Mars_Express/index.html.
Late last month, space and astronomy blogs and news sources were abuzz over the discovery of what may be the most distant event ever detected in the Universe.
The event was something referred to as a Gamma Ray Burst officially designated as GRB 090429B, and it was detected by the ‘Burst Alert Telescope’ which is part of NASA’s ‘Swift’ space satellite. The satellite, launched in 2004, orbits at an altitude of 600 km above the Earth. Here, I take a closer look at what a “gamma ray burst” really is and why this observation is interesting.
A whole lot of “bursting” going on?
First of all, what is all this “bursting” about and why is it important to astronomers? Gamma ray bursts (or GRBs) are really huge energetic explosions, which as the name suggests produce gamma rays. Gamma rays have the smallest wavelengths and highest energies of any other wave in the electromagnetic spectrum. On Earth, they are produced in nuclear explosions as well as by radioactive atoms. In fact, we use gamma rays on Earth because their high energy means that they can kill living cells. In cancer treatment, radiotherapy involves using targeted gamma rays to destroy cancerous cells.
The discovery of Gamma Ray Bursts coming from space was actually more to do with chance than anything else. During the 1960s, the United States Air Force launched a series of satellites, (known as the Vela satellites) to monitor compliance with the Nuclear Test Ban Treaty. These satellites were sensitive to gamma radiation, since a nuclear blast in the Earth’s atmosphere would produce a large amount of gamma-rays. However a strange thing happened: the detectors onboard the satellites began to pick up intense bursts of gamma rays which were very different to those expected– rather like a flashlight shining brightly for a short time, coming from random directions in the sky. By the early 1970’s GRB’s had been discovered. It wasn’t until the early 1990’s though that scientists were able to conclude that these burst events were coming from deep space – with cosmological distances i.e distances ranging from hundreds of millions to billions of light-years away. Despite how very luminous these explosions are, don’t expect to witness one in the night sky. Most of the energy reaches us as gamma rays and our human eyes simply aren’t sensitive to this form of radiation: in short – we can’t see them. In addition, the Earth’s atmosphere does not allow gamma rays to penetrate so we have to rely on space-borne satellites to make observations.
What do we know about Gamma Ray Bursts now?
We now know a lot more about these bursts of light. They can last anywhere from a few milliseconds to a few minutes with most lasting in the 20-40 second range. The initial burst is usually followed by a longer-lived “afterglow” emitted at longer wavelengths (X-ray, ultraviolet, optical, infrared ,etc.) The light itself is extremely bright – hundreds of times brighter than an average supernova and about a million trillion times as bright as the Sun. In fact, GRBs can release more energy in 10 seconds than the Sun will emit in its entire 10 billion-year lifetime.
Because they are the most energetic form of light in the universe, they are only produced in the very hottest regions. Most GRBs occur when a massive star at least 30 times the mass of our Sun, dies (runs out of fuel). These stars collapse dramatically to form black holes or neutron stars and when they do, a huge burst of high energy gamma rays and particles gets ejected in an explosion. Most of this energy is focussed into two distinct ‘beams’ which race out through space heating everything in their path, producing the aforementioned “afterglow effect”. The fact that GRBs (unlike supernovae) shoot out radiation in these narrow beams like a laser make them more difficult to observe – depending on which direction the beams are pointed. These gamma-ray bursts, appear like cosmic flashbulbs from any direction, flicker, and then fade after briefly dominating the gamma-ray sky:
To put it in perspective, GRB’s are the brightest events in our Universe since the Big Bang. Currently orbiting satellites detect an average of about one gamma-ray burst per day. Because gamma-ray bursts are visible to distances encompassing most of the observable universe, which is home to many billions of galaxies, this suggests that gamma-ray bursts must be very rare events per galaxy. Perhaps occurring at a rate of a few, per galaxy per million years. So far, astronomers have found most GRBS detected originate in distant galaxies. And this is precisely why this new detection of a GRB is important. When something is so bright – we can observe it even when we may not even be able to observe light from the galaxy containing the GRB. So GRB’s allow us to measure distances in space greater than we have ever been able to before. Because light travels at a constant, finite speed – this also means that the farther away we see something in the Universe, the further back in time we are looking. If the Universe is assumed to be 13.7 billion years old then the light from the very first stars will take approximately 13.7 billion years to reach us. So the very farthest object we could ever see would be 13.7 billion light years away.
Bring in GRB 090429B
And so we get to last month’s announcement at the American Astronomical Society meeting that astronomers may have discovered the most distant object in the Universe: GRB 090429B. Okay, so perhaps not a name that encompasses how important this may be. Perhaps a picture will help:
Again, perhaps not what we expect as the image of a massive exploding star in the throes of death. However, this is the actual image that NASA’s Swift satellite snapped of the Gamma Ray Burst. Given that this GRB lasted a mere 10 seconds, it is clear how important it is to have a satellite like Swift which slews quickly to point at the source of a GRB within seconds of detecting the burst. Unlike many NASA satellites, “Swift” is not an acronym but instead refers to this ability to quickly change angle and position. Swift is also equipped with X-ray, UV and optical telescopes which measure the “afterglow” of the GRB. What we actually see in the image above is this “afterglow”.
How far away is this thing?
Calculations have estimated the distance to GRB 090429B at 13.14 billion light years. Yes, billion. I mentioned earlier that the age of the Universe is an estimated 13.7 billion years, and so the furthest object we could see would be 13.7 billion light years away. This also means the universe had only been around for a mere 600 million years when this massive explosion took place. The galaxy which contained the GRB was possibly one of the very first formed after the Big Bang- in fact it may still have been in the process of forming when this burst occurred! And on April 29, 2009, courtesy of the Swift satellite – we saw it! (The numerical designation 090429B actually tells us when the GRB was observed.) You can tell by the lapse in time between observation and the announcement last month that painstaking analysis was required to give scientists enough confidence in the data that they believe that this GRB event did in fact happen 13.14 billion years ago, at a distance 96% of the way to the furthest we could ever hope to observe.
How did scientists calculate this distance?
How on earth are we able to say that this could be the most distant object or event in the Universe to date? Astronomers commonly use the term “redshift” to give an idea of how far away an object in space is from us. This is based on the more familiar Doppler effect where wavelengths are stretched out as an object moves away from us. When light travels from the vast distance we are talking about here, we refer to a different type of redshift – the cosmological redshift. This redshift is actually caused by the expansion of space. The wavelength of light increases as it traverses the expanding universe between its point of emission and its point of detection by the same amount that space has expanded during the crossing time. At huge distances, far ultraviolet light for example gets stretched or redshifted all the way into the visible part of the spectrum. We can observe this light that reaches us with ground based telescopes, and by looking at how the wavelength of the light has changed we can calculate how far it has travelled!
In this case, because the light travelled so far much of the UV radiation is absorbed by gas in the universe which the visible light from the burst passed through. The visible light gets redshifted all the way to the infrared. So if the light really had travelled this enormous distance we’d expect to see no visible light (formerly UV light) from the GRB at the earth, but we would see the infrared light that started off its journey as visble light. It turns out this is exactly what we saw, which suggests we are looking at something very distant that happened very early on in the life of our universe.
Ideally, astronomers would measure a complete spectrum of the afterglow of the GRB using several ground based telescopes but thanks to bad weather – this wasn’t possible in this case, making a precise distance measurement difficult. Because GRB’s are so short lived, time is of the essence. However the research team (led by former Penn State University graduate student Antonino Cucchiara) did gather data from the Gemini telescope in Hawai’i and were able to combine this with data from other telescopes which they feel has given them a good level of confidence in estimating the distance to GRB090429B.
Another key piece of information is the fact that astronomers were never able to detect anything in the spot where they saw the afterglow . “We looked with Gemini, the Hubble Space Telescope and also with the Very Large Telescope in Chile and never saw anything once the afterglow faded.” said Cucchiara. “This means that this GRB’s host galaxy is so distant that it couldn’t be seen with any existing telescopes. Because of this, and the information provided by the Swift satellite, our confidence is extremely high that this event happened very, very early in the history of our universe.” Astronomers tend to quantify large distances in terms of this redshift, ‘z’, where higher values of z indicate greater distance and greater lookback time into the early universe. The previous GRB record holder has an estimated z value of around 8.2, with GRB 090429B estimated at 9.4.
So is this REALLY, DEFINITELY, ABSOLUTELY the most distant object ever observed?
It is definitely a convincing candidate but ask some of the Hubble Space telescope astronomers and cosmologists and they may have a different answer. As with all things astronomy, there is a lot of error and uncertainty. Swift’s principal Investigator, Antonino Cucchiara puts it like this: “Like any finding of this sort there are uncertainties. However, if I were in Vegas, I would never bet against the odds that this is the most distant GRB ever seen and we estimate that there is even a 23% chance that it is the most distant object ever observed in the universe.”
Whether or not GRB 090429B is the most distant object we’ve observed to date, the observation itself is a testament to the sensitivity and advancement of both space satellite and ground based telescope technology. Who knows how much further back in time and out in space we’ll be looking in the coming years?
The Alpha Magnetic Spectrometer (or AMS-02 for short) instrument is a cutting edge particle physics experiment which will make its way to the ISS for installation aboard shuttleflight STS-134, scheduled for launch on April 29th. This space based experiment is being led by Nobel Laureate Samuel Ting of the Massachusetts Institute of Technology (MIT).
According to a NASA press release in August, the AMS-02 will “use the unique environment of space to advance knowledge of the Universe, leading to a better understanding of the universe’s origin by searching for antimatter, dark matter, strange matter and measuring cosmic rays.”
So. Everybody clear on that then?
For those without a strong background in particles physics or cosmology, the jargon filled press releases and summaries of this important experiment are not easy to decipher. Not surprising when you consider that this project has involved over 500 physicists from 56 institutes representing 16 countries. That is an extremely large collaboration and this article aims to make the goals and science behind the AMS-02 project easier to understand. Perhaps then the excitement being felt in the physics world about the potential results from the AMS-02 can be shared by all.
Orbiting the Earth on the ISS at an altitude of about 300 km, AMS-02 will study with an unprecedented accuracy of one part in 10 billion the composition of primary cosmic rays, exploring a new frontier in the field of particle physics, searching for primordial antimatter and studying the nature of dark matter.
We can break down three main scientific goals of the AMS-02 experiment as follows:
Cosmic rays: Understanding the cosmic ray environment in space and making precise measurements of the composition and flux (essentially the rate at which a surface is bombarded) of these particles.
Searching for Dark Matter or “missing matter”
Searching for Antimatter
Searching for the “strangelet”
I will outline the basic science behind these goals in the sections below.
To understand the first goal, we need to understand what a “cosmic ray” really is.
Cosmic rays are very energetic particles which come from anywhere in space (i.e. anywhere outside our Earth’s atmosphere) They are particles which travel individually so the term “ray” which suggests a beam of particles together is misleading. Cosmic rays are constantly bombarding the Earth’s atmosphere. The majority of cosmic rays (around 89 percent) are simple protons that travel incredibly fast – near to the speed of light. Another 10% of these particles are so called “alpha particles” which are actually the nuclei of Helium atoms. Less that 1% of the particles are electrons (which we term “beta particles”). The remaining fraction is made up of the other heavier nuclei which are abundant end products of stars’ nuclear synthesis. All of the natural elements in the periodic table are present in cosmic rays, in roughly the same proportion as they occur in the solar system.
The term “cosmic rays” usually refers to Galactic Cosmic Rays, which originate in sources outside the solar system, distributed throughout our Milky Way galaxy. However, these particles can also originate from as nearby as our Sun.
The sheer speed of these particles means that they can easily penetrate matter. When cosmic rays hit the Earth’s atmosphere they collide and react with the atmospheric gases and produce a “shower” of particles with far less energy. These particles are called “secondary cosmic rays” and every piece of matter on Earth is constantly being hit with these incoming particles- including humans. Luckily for us, the secondary cosmic rays have so much less energy than the original primary cosmic rays that impinge on our atmosphere , that we suffer few ill effects. Astronauts in space however do not have the benefit of this protection and so methods to shield humans from cosmic rays during long term space exploration missions require an excellent understanding of these particles.
The main focus of cosmic ray research has been directed towards investigating where cosmic rays originate, how they get accelerated to such high velocities, what role they play in the dynamics of the Galaxy, and what their composition tells us about matter from outside the solar system. To measure cosmic rays directly, (i.e before they have been slowed down and broken up by the atmosphere), research is carried out by instruments carried on spacecraft and high altitude balloons, using particle detectors similar to those used in nuclear and high energy physics experiments.
The AMS-02 is one such detector. Without the atmosphere in the way, primary cosmic rays can be studied like never before. Also up until now most cosmic ray studies are done by balloon-borne satellites with flight times of days. Even on such a brief time scale we have seen great variation. With a nominal mission time of 3 years, the AMS-02 can gather an enormous amount of accurate data and allow measurements of the long term variation of the cosmic ray flux over a wide energy range.
Roberto Battitson, the AMS’ deputy principal investigator has said this of the experiment: “This is the Hubble Space Telescope for cosmic rays. In this category, we are definitely the most sophisticated experiment ever sent to space.”
The Mystery of Dark Matter
If you’ve read popular science books or tuned into the latest documentaries about our universe, chances are you’re heard the terms “dark matter” and “dark energy” at some point. But what is all this dark stuff we keep hearing of and why is it so important?
We use the term “dark” for anything we can’t detect by the radiation it emits or reflects. When we talk of the “matter” in the universe we usually think of what we can see: stars and galaxies. These luminous objects have usually been considered as the most significant collections of matter in our universe.
Amazingly this “ordinary” matter can only account for about 5% of the total matter in the universe. That means that there’s another 95% of something out there that we just can’t see. This 95 percent is dark, either dark matter, which is estimated at 23 percent of the mass of the universe, or dark energy, which makes up the balance. We still do not know the exact nature of both these dark components .
In the words of AMS’ Robert Battitson “Never in the history of science were we so aware of our ignorance: we know that we do not know anything about what makes up 95% of our universe”
So how do we know it’s there if we can’t see it?
By its gravitational force. Anything that has mass also exerts a gravitational force.
Dark matter and Dark Energy are not the same thing. In fact, they can be regarded as opposing forces – each necessary to explain the effects we see in the Universe. Dark matter is thought to be the “stuff” that binds stars and galaxies together, while dark energy exerts a repulsive force driving galaxies further and further apart from each other. Understanding this universal “tug of war” could reveal the ultimate fate of our Universe.
The AMS-02 will be helping in the search for Dark Matter from the unique environment of space.
Dark Matter is unlike anything we have encountered on Earth. It doesn’t emit or reflect light and yet its presence seems to be evident everywhere we look in space.
When we observe certain objects in our universe they behave as though there must be a lot more mass there than we can detect. For example, spiral galaxies spin faster than they should, and clusters of galaxies stick together even though the velocities of their constituent galaxies suggest they should be flying apart. Dark matter also reveals itself when its gravitational mass causes the trajectories of light from stars to bend making the positions of the stars seem to differ from their “true” positions.
Scientists have answered this problem by proposing the existence of some hidden mass – “dark matter”. This solution is widely accepted despite the fact that nobody has ever seen it and nobody is quite sure what it might be. You could say dark matter has been indirectly observed but never captured. The hunt for a dark matter particle continues to accelerate and has become a Holy Grail of particle physics research.
Physicists do have some suggestions as to what form this “missing matter” might take. One candidate you may have heard of is the WIMP or “Weakly Interacting Massive Particle.” These are a class of particles that, as their name suggests, interact via the weak nuclear force and have mass. A popular WIMP is the neutralino. More on that later.
To add to the WIMPS, we also have the possibility of MACHOS (Massive Compact Halo Objects). These objects are less confusing because they are made up of protons and neutrons just like you and I. The term “halo” just refers to the region of a galaxy in which we tend to find these dim/dark objects. MACHOs can be any non-luminous stellar object, including black holes, neutron stars and brown dwarfs.
Because they have mass, MACHOs can be detected using gravitational lensing – a method that looks at how light coming from a distant star has been bent and distorted by an object. Using this technique, limits have been set on the mass of individual MACHOs in our own galaxy, the Milky Way and it has been found that these objects make up no more than a few percent of the mass in our galactic halo. This is not nearly enough to make up the amount of dark matter we know must be present.
So it seems that dark matter must be mostly made up of matter that is very different from that which we are made.
The most popular hypothesis is that dark matter is made up of particles that were created way back in the very early universe and that are stable enough to have made it to this day. The best candidate particle are the neutrino and it’s superpartner, the “neutralino” mentioned earlier.
Neutrinos are abundant and were created in the early universe in numbers similar to electrons and positrons. For a long time we thought that neutrino did not have any mass but it turns out that they do have a very small mass. Although they are difficult to detect because they travel at the speed of light and do not have an electric charge, we know that they really exist . You can imagine that is a relief amongst all this unknown. Billions of neutrinos are currently bombarding your body but don’t be concerned – you won’t feel a thing!
But there’s a problem. Neutrinos are known as “hot” dark matter because they travel so fast. WIMPS on the other hand did not travel at relativistic (fast) speeds in the early universe and we say they are an example of “cold” dark matter
Why does this matter? Early in the universe there must have been fluctuations in the matter density (the way matter was distributed). Otherwise we would not be able to explain the formation of galaxies (clusters of matter). This isn’t a problem if we consider cold dark matter but hot dark matter would have acted similarly to an iron – smoothing out any fluctuations. This would make it impossible to explain the formations of the structure and galaxies we see today. Again we are stuck with a limit on how much dark matter could be made up of neutrinos.
What next? We have one more candidate so far and that is the axion. But these again are “hypothetical” particles and opinion is highly divided on whether they exist at all.
Indeed, we are left with the WIMP being the favoured constituent of dark matter – and the favourite WIMP is the neutralino. Now, we just need to detect it – and this is where the AMS-02 comes in. If neutralinosexist, they could collide with each other producing excesses of charged or neutral particles which can be detected by AMS-02. Any peaks in the background positron, anti-proton, or gamma ray flux could signal the presence of neutralinos or other dark matter candidates. Two previous cosmic ray experiments: PAMELA (an orbiting satellite experiment launched in 2006) and ATIC (a balloon-borne experiment) have given some evidence that these peaks will be found at energies that the AMS-02 instrument is able to detect.
The Search for Antimatter
According to today’s best theories, when the Big Bang occurred about 15 billion years ago, matter and antimatter were created in equal amounts.
What do we mean by antimatter? Antimatter, as the name implies, can be described as the opposite of ordinary matter. Every particle in the universe has characteristics such as mass and charge. With antimatter, the mass remains constant, but the sign of the charge is reversed. An example is the positron – or positive electron. The positron has the same mass as an electron but a positive charge.
It is therefore surprising that our Earth, the solar system, and our galaxy (the Milky Way) do not contain any antimatter. Where did all the antimatter go?
Theories which attempt to explain the present matter-antimatter “asymmetry” (meaning we see enormously more matter than antimatter) are not compatible with many other measurements. Whether or not antimatter still exists in the Universe is a fundamental question in modern physics and cosmology.
Two possibilities exist: either antimatter completely disappeared during the history of universe, or matter and antimatter have been separated from each other to form different regions of the universe. In the second scenario, we would be located in a region where only matter exists but some antimatter coming from an ‘anti’ region outside our galaxy could still have a chance to reach us. This antimatter would be in the form of anti-nuclei (like anti-Helium, anti-Carbon, etc.). The best way to search for this extragalactic antimatter is to use a particle detector in space – the AMS-02.
The AMS-02 will try to detect and prove the existence of this antimatter. Observing just one antihelium nucleus would provide evidence for the existence of large amounts of antimatter somewhere in the Universe. The sensitivity of the instruments aboard the AMS will allow a larger volume of the Universe than ever before to be tested for the existence of antimatter.
Don’t forget about strangelets!
As if all this Dark matter and antimatter wasn’t strange enough already, the AMS-02 will also be searching for something physicist call a “strangelet”. To understand this we need to know a little about particle physics and quarks.
In the 1960’s Murray Gell-Mann hypothesized the existence of “quarks” as one of the fundamental building blocks of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei.
There are six types of quarks: up, down, charm, strange, top, and bottom. Up and down quarks have the lowest masses of all quarks. Stable matter is made up of two types of quarks: the “up” quark and the “down” quark.
Heavier quarks rapidly change into up and down quarks through a process of particle decay. Because of this, up and down quarks are generally stable and the most common in the universe, whereas charm, strange, top, and bottom quarks can only be produced in high energy collisions (such as those involving cosmic rays and in particle accelerators).
It is however possible that there may be stable matter made up of “up”, “down” and the “strange” quark. Physicists have called such particles “strangelets” and they are yet to be detected. Strangelets can have extremely high mass and a small charge to mass ratio. The AMS-02 could give us a definitive answer as to whether this new and extraordinary type of matter exists!
In April, the Space Shuttle Endeavour and her crew of six will make a final flight to the International Space Station. Fans of NASA’s human spaceflight program have begun to mourn the end of an era in the retirement of the space shuttle.
In other circles, excitement is building over the cargo Endeavour will be delivering to the ISS – the Alpha Magnetic Spectrometer or AMS-02 for short. The AMS-02, a state of the art particle physics experiment, represents a scientific collaboration of 56 institutions from 16 countries under the banner of the United States Department of Energy (DoE).
And it’s kind of a big deal.
In fact, groundwork for the AMS-02 began back in 1994. And now we stand mere weeks away from its final deployment and installation on the ISS. A particle detector outside of Earth’s shielding atmosphere offers opportunities and potential results that could change our understanding of the makeup of our Universe.
Over the coming days and weeks, this blog will cover everything you could want to know about the AMS-02. What is it? How does it work? Why should we care? What do we mean by “particle detector” anyway? And of course I’ll be delving into the science behind this ground-breaking experiment.
In this era of uncertainty and change, NASA is still presenting us with new and intriguing ideas, opportunities, technology and science. And that is something to get excited about.
This week NASA’s Fermi space telescope made a discovery that is perplexing scientists around the world. Fermi is a space telescope which detects gamma ray radiation – the most energetic form of electromagnetic radiation. In fact it is billions of times more energetic than the type of light visible to our eyes.
This means that Fermi sees the immense energy of the most exotic and energetic phenomenon in our Universe: super massive black holes, pulsars and streams of hot gas travelling at close to the speed of light. This week Fermi and the astronomers at the Harvard -Smithsonian Center for Astrophysics discovered an astounding structure right in our own Galactic back yard. They discovered huge gamma ray emitting “bubbles” which can best be shown in this image:
The purple bubbles show this incredible and unexpected structure in our Galaxy. Here we are looking at our Milky Way Galaxy edge-on with the “bubbles” emanating from the center. The structures extend 25,000 light years (see box below)to the North and South of the center of our Galaxy. That is quite a significant structure not to have been aware of, but many astronomical phenomenon do not show themselves unless we use the right wavelength of light to detect them – in this case: gamma rays.
A light year is the distance that light travels in one year. One light year is 5,865,696,000,000 miles or 9,460,800,000,000 kilometers.
In total the two bubbles span 50,000 light years or half the diameter of our Galaxy. They have well defined edges and are expanding at a rate of about 2.2 million miles per hour. As mentioned already, gamma rays are emitted from the most energetic things in the universe and here we are looking at structures that hold the energy of about 100,000 supernovae. Earlier surveys aimed at detecting X-ray emission gave a hint to some sort of structure which astrophysicists assumed may also emit gamma rays. They did not however expect anything like the scale of these huge bubbles.
So what in the world (or more aptly, Galaxy) could possibly have produced so much energy?
So far astronomers are considering two possible explanations.
One explanation suggests that at some time there was a “burst” of star formation occurring near the center of the Galaxy which may have produced massive short-lived stars which in turn produced energetic winds (like a much stronger version of our Sun’s “solar wind”) capable of blasting high energy particles out into space and forming these gamma ray bubbles.
Doug Finkbeiner, an astronomer with the Harvard Smithsonian Center for Astrophysics and part of the team that made the discovery, suggests another option may be more plausible. This one is even wilder – and involves an outburst from the supermassive black hole that lives at the center of our own Milky Way. Most if not all, galaxies are thought to harbor a black hole at their center and many of these black holes are associated with high energy “jets” which eject material out of the black hole. This illustration (left) shows the concept of a black hole where there is a spinning disk of material being drawn into the black hole (the accretion disk) and at the same time powerful jets shooting high energy particles out of the back hole in opposite directions.
There is a catch – our Galaxy’s black hole is not see to possess these high energy jets. But at 400 million times the mass of the Sun, our own “local” black hole has probably been very active in its past.
In fact, these bubbles may be the first real “evidence” of an outburst at some time in the past where the black hole was accreting material at such a rate that it was spewing high energy particles back out in the form of jets which formed the structures we are now seeing – these so-called “Fermi bubbles”. Estimates suggest it would only take a period of 10,000 to 100,000 years to produce enough energy to create these structures. (Our Galaxy is about 13.2 billion years old!)
At any rate, it is exciting to have Fermi reveal to us such enormous structures which may have been part of our Galaxy for millions of years.
Sometimes, all you need is a fresh set of (gamma ray sensing) eyes.
NASA’s Fermi is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States. Read more about Fermi at: http://fermi.gsfc.nasa.gov/
The research discussed has been accepted for publication in The Astrophysical Journal
There is plenty of excitement for NASA this week with both manned and unmanned missions sharing the limelight. Avid shuttle watchers are eagerly awaiting this week’s scheduled launch of Space Shuttle Discovery’s final mission to the International Space Station now scheduled for Nov.5th at the earliest.
Nov. 4th held a real treat: NASA’s EPOXI mission made a very successful close encounter with a comet known as Hartley 2. In fact this encounter is the closest a man-made object has ever come to any comet – coming within 435 miles/700 km. This is only the fifth time a spacecraft has “visited” a comet in this way. Many may recall the “Deep Impact” mission which launched in 2005 and aimed to rendezvouz with comet Tempel 1. It did just that on July 4th, 2005. That mission involved the spectacular release of a washing machine-size probe, known as the “impactor,” which collided with the comet, releasing material which was imaged by the Deep Impact spacecraft (which is, in comparison approx the size of a VW beetle).
Scientists used the data and spectra they observed as a means of better understanding the nature and composition of the comet. Although the Deep Impact spacecraft had completed its mission, NASA scientists saw potential for continuing to use the still functioning craft and set about determining a new scientific adventure for the probe. After realizing that a new mission could be accomplished using the same imaging equipment, scientists decided on a new target – the comet Hartley 2.
Hence the EPOXI mission was born. Same spacecraft, different set of of targets – which is why you may be hearing the term “Deep Impact” frequently when listening to coverage of the mission. EPOXI is actually a combination of two scientific investigations. The new mission name “EPOXI” comes from combining two scientific investigations being undertaken by the spacecraft:
EPOCH: Extrasolar Planet Observation and CHaracterization
DIXI: the Deep Impact eXtended Investigation of comets
So it came to be that the original $252 million dollar spacecraft was to fly an additional 2.9 billion miles (4.6 billion Km) to hunt down Hartley 2 arriving 5 years later on Nov. 4th 2010. During it’s time cruising between these comets, the Deep Impact spacecraft completed the Extrasolar Planet Observation and Characterization part of it’s mission objective: primarily a search and study of extrasolar planets and moons.
Catching comet Hartley 2 was to be significantly more challenging than the approach to Tempel-1 because it is about a seventh of the size at roughly 1.25 miles across (2 km) and yet still releases about the same amount of material into space. This makes the comet “flit around the sky” according to mission navigator Shyam Bhaskaran of NASA’s Jet Propulsion Laboratory. In fact the comet moves so much that three maneuvers were needed to adjust the spacecraft’s course – the latest last minute maneuver was 2 days ago!
Finally, yesterday at 10:10am EDT, the EPOXI spacecraft reached it’s goal, flying past Hartley 2 at a distance of 435 miles. The comet came by the EPOXI craft at 12.3 km/s or more than 27, 000 miles per hour.
The flyby went off without a hitch and within an hour 5 spectacular high resolution images arrived at Earth:
Scientists plan to use the extensive data they will receive from its imagers ( two operating at visible wavelengths and one in the infrared) to study the structure of the nucleus and compare it with observations of other comets. Other important questions include what makes this comet so active? Which parts of the comet are emitting gas and what is the nature of these chemicals? With such detailed imagery we may be able to link the activity we observe (jets of gas being emitted) to distinct structures of the nucleus.
The excitement in being able to answer such questions relates to our desire to better understand our Solar System. Since comets are leftovers from the solar system’s early days, this knowledge could reveal a great deal about how our cosmic neighborhood came to be.
Expect more- much more in the coming months. Today’s flyby and the approach leading up to it have already provided a mountain of data for scientists and by Thanksgiving when EPOXI will shift it’s gaze from Hartley 2, scientists expect around 120,000 comet images to have been downloaded to the scientists computers.
NASA scientists have said that they feel that by reusing the Deep Impact spacecraft in this extended mission they have succeeded in getting a very good deal. Although extending the mission into EPOXI has cost an additional $45 million, Ed Weiler, associate administrator at NASA’s Science Mission Directorate has said that this amounts to about 10 percent of what it would have cost to launch a whole new mission. In his words: “The spacecraft has provided the most extensive observations of a comet in history.” “Scientists and engineers have successfully squeezed world class science from a re-purposed spacecraft at a fraction of the cost to taxpayers of a new science project.”
So what is next for Deep Impact and EPOXI? Sadly the Deep Impact spacecraft is running out of fuel, so whether it will remain as a stationary observing platform or set it’s sights on another comet is unknown at this time. As for comet Hartley 2, its days are numbered too. Although it will continue to zip around the Sun for a while longer, (it orbits the Sun once every 6.5 years) it seems the sun is “cooking” 3 to 5 feet (1 to 1.5 meters) of material off the comet’s surface on each orbit. With its smallest side measuring about 1650 feet (500 m), Hartley 2 will not be around for very much longer.
Whatever the future holds the Deep Space/EPOXI mission has certainly shown us a new way to think about “recycling”, NASA style. Rethinking and repurposing missions to get the most science for our buck – that’s something I think we can all get behind.
Last year the infamous NASA LCROSS mission gained attention as the unmanned space probe was set on a collision course with the lunar surface. On October 9 2009, viewers watched as footage of the crash event was streamed back to Earth. The mission crashed a rocket into the moon’s southern pole while the LCROSS craft with all the sensors and recording equipment followed behind, analyzing the cloud of material kicked up by the impact, looking for water. And water was found: on November 13 2009, scientists confirmed the presence of water in data collected from the mission.
It seems that sometimes you just have to be there. Being in direct contact with the subject of research (termed “in situ” observations) has its benefits.
Amateur astronomers lined up telescopes and hundreds of people watched the LCROSS impact on the internet. Although not visually as exciting as many hoped for, the data obtained seems to have justified NASA’s methods of “bombing the Moon” as so many media outlets described. If you were underwhelmed by LCROSS, hold onto your hats because NASA is at it again. And this time it’s shooting for the stars. Or star, actually: our Sun.
NASA’s “Solar Probe Plus” (SPP) is slated for launch in 2018 and involves sending an unmanned probe into the Sun’s atmosphere (the corona) in order to better study its properties. The probe itself will be roughly the size of a small car and as you might imagine, will face scorching temperatures during the planned 6 year, 321 day mission.
At its closest approach the SPP will come within 4 million miles from the Sun’s surface where it will be subject to intense bursts of radiation and temperatures in the range of 2550 degrees Farenheit (1399 °C, 1672 K). Compare this with the previous record-setters for closest solar approach, the Helios probes, which came within roughly 27 million miles (43.5 million km) of the Sun in 1976. At SPP’s closest approach, the intensity of solar radiation that it will experience is over 500 times greater than at the Earth’s distance from the Sun.
To protect the SPP from such intense temperatures, the probe will be equipped with a revolutionary carbon-composite heat shield to protect it during its fiery orbits. This material will be similar to that which protects the Space Shuttle from the heat of atmosphere reentry. The probe itself will be solar powered, getting its electricity from liquid-cooled solar panels that can retract behind the heat shield whenthe sunlight becomes too intense.
Before the science can begin, the Solar Probe Plus has a journey ahead to bring it into an oval orbit around the Sun. This involves 7 “fly-by” approaches to Venus to adjust its orbit. This can be seen as the opposite of the traditional “gravity assist” where probes like Cassini have orbited planets to increase their speed so as to reach further out into the Solar System. When we send spaceprobes towards the Sun, they are greatly accelerated by the Sun’s gravitational well and so they must be slowed down to enter into a useful orbit. As the schedule stands, the SPP would make its closest approach to the Sun in late 2024. During its 24 orbits of the Sun the probe comes ever closer to the Sun so that at its closest position it will be well within Mercury’s orbit, about 8.5 solar radii or 3.7 million miles from the Sun’s surface. This is 7 times closer than any previous spacecraft.
Another first will be its speed of orbit: on its closest approach the SPP will be flying past the sun at a speedy 125 miles per second (450 000 mph, 724000 km/h).
That’s fast. Roughly 3 times as fast as any other space probe has travelled. Compare with the Space shuttle and International Space Station which orbit the Earth at approximately 17,500 mph (28000Km/h).
Five scientific experiments have been selected for the mission and range from counting the most abundant particles present in the solar wind to a telescope that will make 3D images of the Sun’s corona.
So why the Sun? Don’t we already know a lot about our closest star? The answer is yes – and no. Some important questions which scientists studying the Sun (heliophysics) have been searching for answers to for decades remain.
Two of the most important of these questions may be answered by NASA’s Solar Probe Plus mission:
Why is the sun’s outer atmosphere, the corona, so much hotter than the sun’s visible surface? (the coronal heating problem)
What drives the solar wind – the streams of highly energetic particles that blow out at speeds of a million miles an hour, affecting the Earth and entire Solar System
In addition, during its time orbiting the Sun, the SPP is likely to encounter several “solar storms”. Researchers suspect that many of the most dangerous particles produced by solar storms are energized in the corona—just where Solar Probe Plus will be. The spacecraft will have an up close and personal view of these Solar Energy Particle (SEP) events, enabling scientists to better understand, characterize and forecast the radiation levels that might threaten the heath and safety of future space explorers.
I go into some of the science involved below. This is without doubt an exciting mission and the first time humankind has dared to rendezvous with a star. In itself that makes this adventure quite remakable.
Some of the science behind the mission
The first of the two questions stated above arises when we look at the Sun’s composition:
The Sun’s Core is at a temperature of approximately 13.6 million Kelvin (~25 million degrees Farenheit). The optical surface of the sun (the photosphere) is known to have a temperature of approximately 6,000 K ( 10340 degrees Farenheit, 5700°C). Above it lies the solar corona, rising to a temperature of 1,000,000–2,000,000 K.
Herein lies the problem: how can the corona of the sun be millions of kelvin hotter than the lower surface of the sun (photosphere)?
The second law of thermodynamics can be stated in the form attributed to Rudolf Clausius:
“Heat generally cannot flow spontaneously from a material at lower temperature to a material at higher temperature.”
In other words, heat would normally be unable to flow from the solar photosphere to the hotter corona, so we must conclude that something other than direct heat conduction must be responsible for the high temperatures in the corona.
At present the two theories considered the most likely involve
1) Wave heating
Several different types of waves can exist in the Sun’s plasma environment and are similar to sound waves in air. Two specific types of waves: Alfvén waves and magneto-acoustic waves could potentially carry energy from the Sun’s photosphere up into the corona. However, magneto-acoustic waves seem unable to carry enough energy upwards into the corona without being reflected back to where they came from due to low pressure.
And Alfvén waves may reach the corona but dissipate energy far too slowly and insufficiently to account for how much heating we observe.
We’ve also seen quite a lack of direct observations of uniformly energetic waves in the Sun’s corona so far — which we’d expect if the theory holds true.
2) Magnetic reconnection (nanoflares)
This theory relies on the Sun’s magnetic field present in the Corona. In fact, as well as the magnetic field loops we associate linking active parts of the Sun, we now know that the Sun’s entire surface contains small “patches” of magnetic fields. A patchwork of small magnetic fields and loops, now dubbed the “magnetic carpet”, can appear and disappear again on timescales on the order of ~40 hours (see figure below).
A magnetic field induces an electric current (as we see in generators). Sometimes in a plasma, their electric currents “collapse” and the magnetic field lines which were maintained by those currents “reconnect” to other poles and energy is released as waves and heat.
No one really knows what could produce these magnetic patches, which vary on such short timescales. Professor Edward Spiegel from Columbia University has suggested that the patches are produced by small dynamos located just beneath the surface of the Sun. But there is no proof so far.
It is also possible that a combination of these theories provides the answer.
The second question that the Solar Probe Plus hopes to shed light on is that of how the solar wind is driven. The solar wind streams off of the Sun in all directions at speeds of about 1 million miles per hour (400 km/s). Originating in the corona, the temperature of the solar wind helps it escape the sun’s gravity. Determining how the corona is heated is important in also understanding how and where the coronal gas is accelerated to such high velocities. Additionally the solar wind is NOT uniform and has both slower and faster components. Determining the mechanisms for both the slow and fast components of the solar wind is of great scientific interest.
In both problems, the fundamental role of the sun’s magnetic field in shaping dynamical processes on all scales has become very apparent.
Want to know more about spacecraft that have crashed into or landed on solar system bodies? Check out a list here