Ahh, another beautiful photograph captured by the Hubble Space Telescope. This time we’re looking at two big, beautiful spiral galaxies… tearing each other apart. The large, face-on spiral is NGC 3808, while its dueling partner is the smaller, edge-on NGC 3808A. And between the two is a long today tail of stars, gas and dust, transferring from one to the other.
The two galaxies are collectively known as Arp 87; just one of the hundreds of interacting galaxies seen by astronomers. It was cataloged by the famous Halton Arp in the 1960’s, who maintained his Atlas of Peculiar Galaxies. And this collision is plenty peculiar, thanks to Hubble’s optics and resolution of fine details.
A stream of gas, stars and dust is flowing from NGC 3808 to its companion, enveloping it in a starry embrace. Because the NGC 3808A is seen nearly edge-on, you can make out the twisting trail of stars wrapping around it. Both galaxies have been distorted by their gravitational interaction.
When galaxies interact, stars are born. And this is the case for Arp 87. The colour of the stars and the intensity of heated interstellar dust show that both galaxies are undergoing furious rates of star formation.
Out there, in the darkness of space, a galaxy is committing a robbery. The robber, known as 3C 326 North is a galaxy the size of our Milky Way. Its victim contains about half the mass, and that’s going steadily down, because 3C 326 North is stealing some of its gas away.
The galactic interaction was revealed by NASA’s Spitzer Space Telescope. These kinds of interactions are common across the Universe; however, this is one of the clearest examples ever seen. The mass of more than a billion suns is being heated up and siphoned away, from the smaller galaxy to the larger one.
According to Patrick Ogle, a researcher at NASA’s Spitzer Space Center, “this could be an important phase in galaxy mergers that we are just now witnessing.”
Ogle and his collaborators were initially trying to study a set of distant objects called radio galaxies, located about a billion light-years away. These are named for the torrent of radio waves pouring out of the supermassive black holes at the centres of the galaxies. 3C 326 North was just the most extreme of the bunch.
When they studied the interacting pair further, they noticed it had a tail of stars, connecting the two objects together. Here’s Ogle again:
“The galaxy in question appears to be stripping a large quantity of molecular hydrogen from its neighbor and heating it up,” said Ogle. “The supermassive black hole at the center of the galaxy is digesting a small fraction of the gas and ejecting it in enormous, relativistic jets millions of light-years long.”
In the near future, the older, larger 3C 326 North will experience a second youth. The stolen gas will give it renewed pockets of star formation. The smaller 3C 326 South will have that youth stolen from it – it’ll no longer be able to form stars on its own. In the far future, the two galaxies may eventually merge, and then all will be forgiven.
Look at the picture associated with this story. It just looks like a pretty galaxy, right? Well, according to astronomers, it’s actually much older than it appears. This image, captured by the Hubble Space Telescope, provides one of the most detailed observations ever taken of I Zwicky 18 – a galaxy that looks younger than it should.
According to researcher, galaxies like I Zwicky 18 are much more common billions of light years away, at a time when the Universe was much younger than it is today. These baby galaxies still had large quantities of gas and dust they could use up to make new stars. Their young hot stars, composed largely of primordial hydrogen and helium manufactured during the Big Bang, burn brightly in the blue end of the visible light spectrum.
Older galaxies, like our own Milky Way have had plenty of time to use up those primordial elements, mixing in heavier elements with generation after generation of supernovae.
Astronomers used to think that I Zwicky 18 was a rare example of a nearby, newly forming galaxy. Located only 59 million light-years from Earth, this galaxy could be used as a sort of time machine, to see the stages that galaxies went through early on in their evolution.
Well, the new observations from Hubble have dashed those hopes. I Zwicky 18 is old, possibly as old as the Milky Way, forming its first stars up to 10 billion years ago. With its sensitive instruments, Hubble was able to spot previously hidden red, older stars, showing that the galaxy has been forming stars for billions of years.
So how is it possible that such an old galaxy still has large quantities of primordial hydrogen and helium, but we see rapid star formation today? It’s possible that the galaxy has just been going slowly, forming stars at a dramatically reduced rate in the past. But something kicked that rate of star formation into high gear in the recent past.
The speed of light is the speed of light, and that’s that. Right? Well, maybe not. Try and figure this out. Astronomers studying radiation coming from a distant galaxy found that the high energy gamma rays arrived a few minutes after the lower-energy photons, even though they were emitted at the same time. If true, this result would overturn Einstein’s theory of relativity, which says that all photons should move at the speed of light. Uh oh Einstein.
The discovery was made using the new MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescope, located on a mountain top on the Canary island of La Palma. Since gamma rays are blocked by the Earth’s atmosphere, astronomers have figured out a clever trick to see them from the ground. When the gamma rays strike the atmosphere, they release a cascade of particles and radiation. The Cherenkov technique detects this cascade, and then works backwards to calculate the direction and energy level of the gamma rays. With a 17-metre detector, MAGIC is the largest telescope of its type.
The international team of researchers pointed the telescope at Markarian 501, a galaxy 500 million light-years away that contains a blazar – a supermassive black hole that periodically releases bursts of gamma rays. More material is falling into the black hole than it can consume, and so it gets squeezed into jets that fire off from the poles of the black hole at close to the speed of light. What astronomers call a “blazar” is when the jets of a supermassive black hole are pointed directly at the Earth.
Researchers sorted high- and low-energy gamma ray photons coming from the blazar with each flareup. Since all the radiation was emitted at the same time, and the speed of light is the speed of light, you would expect the high-energy photons to arrive at the same time. But nope, the high-energy photons showed up around 4 minutes later.
So what’s happening? Nobody knows, and this could turn into an entirely new field of physics. The researchers are proposing that maybe the radiation is interacting with “quantum foam”. This is a theoretical property of space itself, and predicted by quantum gravity theory – a competitor to string theory.
It’s not a huge story, just some cool science and a pretty picture. Here’s a newly released image of the Orion Nebula, captured by two of the great observatories: the Chandra X-Ray Observatory and the Hubble Space Telescope. The bright blue and orange points are young stars, blazing out the X-rays visible to Chandra, while the diffuse glow is the surrounding gas and dust revealed by Hubble.
The Orion Nebula is located 1,500 light years away, and it’s one of the closest star forming regions to the Earth. Amateur astronomers often direct their telescopes towards this nebula, since it’s so close, large and bright.
This image was made by combining photographs captured by both Hubble and Chandra. The Chandra data was built up from almost 13 days of continuous observations, and they allowed astronomers to watch the activity of newborn stars, just 1-10 million years old. During the observation period, the stars flared in their X-ray output. Unlike our own Sun, which is pretty boring as stars go, these young stars are violent and chaotic; demonstrated by the fluctuations of radiation pouring off of them. You wouldn’t want to be living on a planet orbiting one of these monsters.
The wispy clouds of gas and dust (seen in pink and purple) are visible light images captured by Hubble. Right now they’re wispy filaments, but their gravitational interaction is bringing together new stars. One day these too will ignite in the warm glow of newly formed stars.
It’s time for another amazing image from Hubble. You’re looking at nebula NGC 3603, one of the most spectacular star forming regions in the Milky Way. It’s located about 20,000 light-years away from the Earth, in the Carina spiral arm. Apart from offering up pretty pictures, this region is important for science too. Birth and death, gas and dust, NGC 3603 has it all.
This Hubble image shows many different things happening, all at the same time. Most of the stars in the image were all born in the nebula, and differ in size, mass, temperature and colour. There are some absolute monsters in there, dozens of times the mass of our own Sun. These huge stars live fast and die young, burning through their hydrogen fuel quickly, and blowing out fearsome ultraviolet radiation. The combined radiation of all the stars has carved out an enormous cavity of gas and dust in the centre of the nebula – the clear region in the middle.
According to astronomers, the most massive stars are concentrated into the centre of the cluster. In fact, three of them seem to have more mass than is theoretically possible. Instead of single stars; however, they might be binary pairs, so close that even Hubble can’t distinguish them. The largest star was measured with a mass of 115 times the mass of our Sun. So, either the observations or the theories are wrong; stay tuned to see how this one plays out.
Around the swirling nebula are some darker regions called Bok globules. These are dark clouds of gas and dust with the mass of about 10-50 times our Sun. They’re under the process of collapsing, and will eventually form stars, but for now they’re some of the coldest objects in the Universe. You need cold gas before you can get hot stars.
The entire nebula seems contain about 400,000 times the mass of the Sun. That’s enough material for plenty of stars.
Carina Nebula. Image credit: Hubble Space Telescope/NASA.
When you look at the amazing pictures captured by the Hubble Space Telescope, or the Mars Exploration Rovers, do you ever wonder: is that what you’d really see with your own eyes? The answer, sadly, is probably not. In some cases, such as with the Mars rovers, scientists try and calibrate the rovers to see in “true color,” but mostly, colors are chosen to yield the most science. Here’s how scientists calibrate their amazing instruments, and the difference between true and false colors.
So, to start off, let’s put this in the form of a true or false question: T or F: When we see the gorgeous, iconic images from Hubble or the stunning panoramas from the Mars rovers, do those pictures represent what human eyes would see if they observed those vistas first hand?
Answer: For the Hubble, mostly false. For the rovers, mostly true, as the rovers provide a combination of so-called “true” and “false” color images. But, it turns out, the term “true color” is a bit controversial, and many involved in the field of extraterrestrial imaging are not very fond of it.
“We actually try to avoid the term ‘true color’ because nobody really knows precisely what the ‘truth’ is on Mars,” said Jim Bell, the lead scientist for the Pancam color imaging system on the Mars Exploration Rovers (MER). In fact, Bell pointed out, on Mars, as well as Earth, color changes all the time: whether it’s cloudy or clear, the sun is high or low, or if there are variations in how much dust is in the atmosphere. “Colors change from moment to moment. It’s a dynamic thing. We try not to draw the line that hard by saying ‘this is the truth!'”
Bell likes to use the term “approximate true color” because the MER panoramic camera images are estimates of what humans would see if they were on Mars. Other colleagues, Bell said, use “natural color.”
Zolt Levay of the Space Telescope Science Institute produces images from the Hubble Space Telescope. For the prepared Hubble images, Levay prefers the term “representative color.”
“The colors in Hubble images are neither ‘true’ colors nor ‘false’ colors, but usually are representative of the physical processes underlying the subjects of the images,” he said. “They are a way to represent in a single image as much information as possible that’s available in the data.”
True color would be an attempt to reproduce visually accurate color. False color, on the other hand, is an arbitrary selection of colors to represent some characteristic in the image, such as chemical composition, velocity, or distance. Additionally, by definition, any infrared or ultraviolet image would need to be represented with “false color” since those wavelengths are invisible to humans.
The cameras on Hubble and MER do not take color pictures, however. Color images from both spacecraft are assembled from separate black & white images taken through color filters. For one image, the spacecraft have to take three pictures, usually through a red, a green, and a blue filter and then each of those photos gets downlinked to Earth. They are then combined with software into a color image. This happens automatically inside off-the-shelf color cameras that we use here on Earth. But the MER Pancams have 8 different color filters while Hubble has almost 40, ranging from ultraviolet (“bluer” than our eyes can see,) through the visible spectrum, to infrared (“redder” than what is visible to humans.) This gives the imaging teams infinitely more flexibility and sometimes, artistic license. Depending on which filters are used, the color can be closer or farther from “reality.”
Stone mountain rock outcrop in true and false colour. Image credit: NASA/JPL
The same rock imaged in true and false color by Opportunity.
In the case of the Hubble, Levay explained, the images are further adjusted to boost contrast and tweak colors and brightness to emphasize certain features of the image or to make a more pleasing picture.
But when the MER Pancam team wants to produce an image that shows what a human standing on Mars would see, how do they get the right colors? The rovers both have a tool on board known as the MarsDial which has been used as an educational project about sundials. “But its real job is a calibration target,” said Bell. “It has grayscale rings on it with color chips in the corners. We measured them very accurately and took pictures of them before launch and so we know what the colors and different shades of grey are.”
One of the first pictures taken by the rovers was of the MarsDial. “We take a picture of the MarsDial and calibrate it and process it through our software,” said Bell. “If it comes out looking like we know it should, then we have great confidence in our ability to point the camera somewhere else, take a picture, do the same process and that those colors will be right, too.”
Hubble can also produce color-calibrated images. Its “UniverseDial” would be standard stars and lamps within the cameras whose brightness and color are known very accurately. However, Hubble’s mission is not to produce images that faithfully reproduce colors. “For one thing that is somewhat meaningless in the case of most of the images,” said Levay, “since we generally couldn’t see these objects anyway because they are so faint, and our eyes react differently to colors of very faint light.” But the most important goal of Hubble is produce images that convey as much scientific information as possible.
The rover Pancams do this as well. “It turns out there is a whole variety of iron-bearing minerals that have different color response at infrared wavelengths that the camera is sensitive to,” said Bell, “so we can make very garish, kind of Andy Warhol-like false color pictures.” Bell added that these images serve double duty in that they provide scientific information, plus the public really enjoys the images.
And so, in both Hubble and MER, color is used as a tool, to either enhance an object’s detail or to visualize what otherwise could not be seen by the human eye. Without false color, our eyes would never see (and we would never know) what ionized gases make up a nebula, for example, or what iron-bearing minerals lie on the surface of Mars.
As for “true color,” there’s a large academic and scholarly community that studies color in areas such as the paint industry that sometimes gets upset when the term “true color” is used by the astronomical imaging group, Bell explained.
“They have a well-established framework for what is true color, and how they quantify color,” he said. “But we’re not really working within that framework at that level. So we try to steer away from using the term ‘true color’.”
Levay noted that no color reproduction can be 100% accurate because of differences in technology between film and digital photography, printing techniques, or even different settings on a computer screen. Additionally, there are variations in how different people perceive color.
“What we’re doing on Mars is really just an estimate,” Bell said, “it’s our best guess using our knowledge of the cameras with the calibration target. But whether it is absolutely 100% true, I think it’s going to take people going there to find that out.”
For more information see http://hubblesite.org/ or check out Jim Bell’s 2006 book “Postcards From Mars.”
It’s not every day that you see something completely new in the night sky. But that’s what Australian and US researchers have announced this week. They uncovered a mysterious burst of radio energy that came from outside our galaxy. It was incredibly bright, emanating from a tiny object, and lasted for only 5 milliseconds. Blink and you would have missed it (actually, don’t bother blinking, you’d still miss it). So, the big question is: what was that?!
Astronomers from Swinburne University and West Virginia University announced their unexpected discovery this week, with an article in the journal Science.
Their discovery was made by chance. The researchers were analyzing radio observations of rotating pulsars – the corpses of massive stars – when they noticed a brief, bright flash of radio waves in their images. They were looking at the Small Magellanic Cloud, a nearby dwarf galaxy, and were fortunate to have the flash occur in their field of view; off to the side away from the galaxy.
Based on their further analysis, whatever made the flash of radio waves is millions of light-years away, well outside the galaxy, and tiny; probably less than 1,500 km across. Objects at this distance should be very faint, but what they found overwhelmed the radio telescope’s detectors.
So what was it?
There are two theories on the table right now. One is a collision between a binary pair of neutron stars. These exotic objects were once stars much larger than our own Sun. After both detonated as supernovae, they spiraled inward towards one another, eventually merging. Astronomers think this event can also cause a certain kind of gamma ray burst, but a flash of radio waves has never been seen before.
Another, even more exotic explanation is the death of black hole. Famed astrophysicist Stephen Hawking proposed that black holes can actually evaporate, losing mass over long periods of time. As the black hole loses mass, the evaporation speeds up, and the last few moments of a black hole could actually go quite quickly, perhaps with a flash of radio waves like this.
Based on the fact that the discovery was a total coincidence, the astronomers are hopeful that this kind of event is happening all over the sky, all the time. Astronomers have just never thought to look for them. It’s possible that this discovery could even open up a whole new field of astronomy, just like when gamma ray bursts were first discovered 30 years ago when the military orbited satellites designed to see nuclear explosions on the Earth.
Original Source: Swinburne University News Release
You can’t keep a good mission down. I guess you can. Actually, it seems like most good missions are kept down (Terrestrial Planet Finder, anyone?). But once, it looks like the good guys are going to win. A cool mission to search for black holes has been resurrected, and will fly in space after all. Wise move NASA, send a spacecraft to help solve one of the most puzzling mysteries in modern astronomy.
The mission is called the Nuclear Spectroscopic Telescope Array, or NuSTAR. NASA was originally planning this mission, capable of detecting nearby black holes with unprecedented sensitivity, but they decided to shelve it because of funding pressures back in 2006.
NuSTAR is part of NASA’s Explorers Program. These are low-cost, regular missions to help solve a specific challenge in astronomy. Previous missions include Swift (for tracking down gamma ray bursts), and GALEX (which performs ultraviolet astronomy). Another mission, WMAP, told us that the Universe is 13.7 billion years old.
If all goes well, NuSTAR will be launched in 2011, bridging the gap between the 2009 launch of the Wide-field Infrared Survey Explorer, and the 2013 launch of the James Webb Space Telescope.
Once in space, it’ll perform deep observations in hard X-rays, searching for the telltale signature of black holes of various sizes and other exotic and extreme objects.
Quick, look at the picture with this story. Are you looking at a comet? Nope, that’s an entire galaxy. But the process is similar. In this case, an entire galaxy is plunging into a galaxy cluster. The interstellar winds are tearing away at its structure, shedding material, and trailing stars behind into a trail 200,000 light-years long. But it’s actually a region of creation, not destruction, as millions of new stars are forming behind the galaxy.
The image you’re looking at was captured by NASA’s Chandra X-ray observatory as well as the Southern Astrophysical Research (SOAR) telescope in Chile. The blue colours are regions bright with X-rays, while the red colours show regions rich in hydrogen gas.
The galaxy is called ESO 137-001, and it’s currently falling into the massive galaxy cluster Abell 3627. The pressure from the intergalactic wind coming from the galaxy cluster is causing gas in ESO 137-001 to heat up to millions of degrees. At the same time, though, hydrogen gas is being stripped out of the galaxy and trailing behind for more than 200,000 light years.
From their observations, astronomers can detect that millions of stars are forming in this galactic tail; the interaction between the gas and intergalactic wind is helping it collapse into massive star forming regions.
By galactic standards, these newly forming stars – most are less than 10 million years old – are going to be very lonely. They’re much further away from their galactic home than stars can ever normally form. Life that might evolve on worlds in those regions would see a few stars in the night sky, and a large haze for their parent galaxy, but otherwise, the sky would seem black.
