Artist's rendering of the Giant Magellan Telescope and support facilities at Las Campanas Observatory, Chile, high in the Andes Mountains. Photo by Todd Mason/Mason Productions
[/caption]
Astronomy organizations in the United States, Australia and Korea have signed on to build the largest ground-based telescope in the world – unless another team gets there first. The Giant Magellan Telescope, or GMT, will have the resolving power of a single 24.5-meter (80-foot) primary mirror, which will make it three times more powerful than any of the Earth’s existing ground-based optical telescopes. Its domestic partners include the Carnegie Institution for Science, Harvard University, the Smithsonian Institution, Texas A & M University, the University of Arizona, and the University of Texas at Austin. Although the telescope has been in the works since 2003, the formal collaboration was announced Friday.
Charles Alcock, director of the Harvard-Smithsonian Center for Astrophysics, said the Giant Magellan Telescope is being designed to build on the legacy of a rash of smaller telescopes from the 1990s in California, Hawaii and Arizona. The existing telescopes have mirrors in the range of six to 10 meters (18 to 32 feet), and – while they’re making great headway in the nearby universe – they’re only able to make out the largest planets around other stars and the most luminous distant galaxies.
With a much larger primary mirror, the GMT will be able to detect much smaller and fainter objects in the sky, opening a window to the most distant, and therefore the oldest, stars and galaxies. Formed within the first billion years of the Big Bang, such objects reveal tantalizing insight into the universe’s infancy.
Earlier this year, a different consortium including the California Institute of Technology and the University of California, with Canadian and Japanese institutions, unveiled its own next-generation concept: the Thirty Meter Telescope. Whereas the GMT’s 24.5-meter primary mirror will come from a collection of eight smaller mirrors, the TMT will combine 492 segments to achieve the power of a single 30-meter (98-foot) mirror design.
In addition, the European Extremely Large Telescope is in the concept stage.
In terms of science, Alcock acknowledged that the two telescopes with US participation are headed toward redundancy. The main differences, he said, are in the engineering arena.
“They’ll probably both work,” he said. But Alcock thinks the GMT is most exciting from a technological point of view. Each of the GMT’s seven 8.4-meter primary segments will weigh 20 tons, and the telescope enclosure has a height of about 200 feet. The GMT partners aim to complete their detailed design within two years.
The TMT’s segmented concept builds on technology pioneered at the W.M. Keck Observatory in Hawaii, a past project of the Cal-Tech and University of California partnership.
Construction on the GMT is expected to begin in 2012 and completed in 2019, at Las Campanas Observatory in the Andes Mountains of Chile. The total cost is projected to be $700 million, with $130 million raised so far.
Artists concept of the Thirty Meter Telescope Observatory. Credit: TMT
Construction on the TMT could begin as early as 2011 with an estimated completion date of 2018. The telescope could go to Hawaii or Chile, and final site selection will be announced this summer. The total cost is estimated to be as high as $1 billion, with $300 million raised at last count.
Alcock said the next generation of telescopes is crucial for forward progress in 21st Century astronomy.
“The goal is to start discovering and characterizing planets that might harbor life,” he said. “It’s very clear that we’re going to need the next generation of telescopes to do that.”
And far from being a competition, the real race is to contribute to science, said Charles Blue, a TMT spokesman.
“All next generation observatories would really like to be up and running as soon as possible to meet the scientific demand,” he said.
In the shorter term, long distance space studies will get help from the James Webb Space Telescope, designed to replace the Hubble Space Telescope when it launches in 2013. And the Atacama Large Millimeter Array (ALMA), a large interferometer being completed in Chile, could join the fore by 2012.
Image where PHA 2009 BD81 (left) was discovered. PHA 2008 EV5 is on the right. Image courtesy Robert Holmes.
[/caption]
While observing a known asteroid on January 31, 2009, astronomer Robert Holmes from the Astronomical Research Institute near Charleston, Illinois found another high speed object moving nearby through the same field of view. The object has now been confirmed to be a previously undiscovered Potentially Hazardous Asteroid (PHA), with several possible Earth impact risks after 2042. This relatively small near-Earth asteroid, named 2009 BD81, will make its closest approach to Earth in 2009 on February 27, passing a comfortable 7 million kilometers away. In 2042, current projections have it passing within 5.5 Earth radii, (approximately 31,800 km or 19,800 miles) with an even closer approach in 2044 2046. Data from the NASA/JPL Risk web page show 2009 BD81 to be fairly small, with a diameter of 0.314 km (about 1000 ft.) Holmes, one of the world’s most prolific near Earth object (NEO) observers, said currently, the chance of this asteroid hitting Earth in 33 years or so is quite small; the odds are about 1 in 2 million, but follow-up observations are needed to provide precise calculations of the asteroid’s potential future orbital path.
In just the past couple of years, Holmes has found 250 asteroids, 6 supernovae, and one comet (C/2008 N1 (Holmes). However, he said he would trade all of them for this single important NEO discovery.
“I was doing a follow up observation of asteroid 2008 EV5,” Holmes told Universe Today, “and there was another object moving right next to it, so it was a pretty easy observation, actually. But you just have to be in the right place at the right time. If I had looked a few hours later, it would have moved away and I wouldn’t have seen it.” A map generated by Holmes showing the path of 2009 BD 81. Credit: Robert Holmes
A few hours later, teacher S. Kirby, from Ranger High School in Texas, who was taking part in a training class on how to use the data that Holmes collects for making observations used Holmes’ data measuring 2008 EV5 and also found the new object. Shortly after that, a student K. Dankov from the Bulgarian Academy of Science, Bulgaria who is part of ARO education and public outreach also noticed the new asteroid. Holmes listed both observers as co-discovers as well as another astronomer who made confirmation follow-up observations of what is now 2009 BD81.
Holmes has two telescopes, a 24-inch and 32-inch. Holmes' 24 inch telescope. Courtesy Robert Holmes
He works night-after-night to provide real-time images for the IASC program, uploading his images constantly during the night to an FTP site, so students and teachers can access the data and make their own analysis and observations from them. IASC is a network of observatories from 13 countries all around the world.
Holmes is proud of the work he does for education, and proud of the students and teachers who participate.
“They do a great job,” he said. “A lot of the teachers are doing this entirely on their own, taking it upon themselves to create a hands-on research class in their schools.” Holmes said recently, two students that have been involved with IASC in high school decided to enter the astrophysics program in college.
“I feel like we are making a difference in science and education,” he said, “and it is exciting to feel like you’re making a contribution, not just following up NEO’s but in people’s lives.”
Holmes also owns some of the faintest observations of anyone in the world.
“My telescopes won’t go to 24th magnitude,” Holmes said, “but I’ve got several 23rd magnitudes.”
“Getting faint observations is one of the things NASA wants to achieve, so that’s one of the things I worked diligently on,” Holmes continued. The statistics on the site bear that out clearly, which shows graphs and comparisons of various observatories.
To what does Holmes attribute his success? “It’s obviously not the huge number nights we have in Illinois to work,” Holmes said. The East-Central region of Illinois is known for its cloudy winter weather, when we often have our poorest astronomical “seeing.”
“However, I work every single night if it’s clear, even if it’s a full moon,” he said. “Most observatories typically shut down three days on either side of a full moon. But I keep working right on through. I found that with the telescopes I work with, I’ve been able to get to the 22nd magnitude even on a full moon night. Last year, I got about 187 nights of observing, which is the same number as the big observatories in the Southwest, when you take off the number of cloudy nights the 6 nights a month they don’t’ work around full moons. Sometimes you just have to work harder, and work when others aren’t to be able to catch up. That’s how we are able to do it, by working every single chance we have.”
He works alone at the observatory, running the pair of telescopes, and doing programming on the fly. “I refresh the confirmation page of new discoveries every hour so I can chase down any new discovery anyone has found,” he said. “If I just pre-programmed everything I wouldn’t have a fraction of the observations I have each year. I’d miss way too many because some of the objects are moving so fast.”
Holmes said some objects are moving 5,000 arc-seconds an hour on objects that are really close to Earth. “I’ve seen them go a full hour of right ascension per day and that’s pretty quick. They can go across the sky in four or five days,” said Holmes. “And there have been some that have gone from virtually 50 degrees north to 50 degrees south in one night. That’s was a screaming fast object, and you can’t preprogram for something like that, you actually have to be running the telescope manually.”
Overhead view of 2009 BD81's path. Courtesy Robert Holmes
2009 BD81 is listed as a “risk” object on the NASA/JPL website. This is the 1,015th PHA discovered to date.
“It ranks high as a NEO in general,” said Holmes, “although not in a super-high category as far as the Torino scale,” which categorizes the impact hazard of NEOs. “At this point it’s considered a virtual impactor and that is typically is as high of a rating that you get at this point.”
“Because it is a virtual impactor, it will remain on that webpage and ask for observations every single night until it is removed as a virtual impactor or becomes too faint to see,” said Holmes. “In the past year, we’ve removed 23 virtual hazardous objects, which means there have been enough observations that the orbit of that object is no longer considered a threat to our planet.” 2009 BD81. Courtesy Robert Holmes
Because of the small number of observations of of 2009 BD81, the current chance of it hitting Earth is small. “The odds are really small right now,” said Holmes, “however, the smaller your orbital arc is the wider the path is at that point is of potential impact. The longer the arc gets, the narrower the cone of opportunity of impact becomes, and once that cone is no longer pointing at earth in the future, it is removed as a possible impactor.”
Holmes said the excitement of this discovery has been exhilarating. “It’s been a lot of fun. The energy level gets pretty high when you have something like this show up,” he said. “It’s pretty rare, and this is the first time I’ve ever had a NEO discovery. I’ve had several hundred asteroids, and just since the beginning of the school year we have had about 40 asteroids that students and teachers have discovered in the program. So having this as a NEO is kind of a nice thing.”
Holmes said he’ll track 2009 BD81 as long as he possibly can.
Holmes previously was a commercial photographer who had over 4,500 photographs published worldwide in over 50 countries. “At first astronomy was just a hobby in the evening,” said Holmes. “I worked with schools, who used the data and made some discoveries of supernovae and asteroids. It came to a point where it was really hard to work all day as a photographer and work all night in astronomy getting data for students.” So, he chose astronomy over photography.
Holmes now works under a grant from NASA to use astrometry to follow-up new asteroid discoveries for the large sky surveys and help students look for new asteroid discoveries for educational outreach programs.
One would assume that as a former commercial photographer, Holmes would attempt to capture the beauty of the night sky in photographs, but that’s not the case.
“The only thing I’m really interesting in is the scientific and educational aspect of astronomy,” said Holmes. “I’ve never taken a single color, pretty picture of the sky in the half a million images I’ve taken of the sky. It’s always been for research or education.”
Holmes is considered a professional astronomer by the Minor Planet Center and International Astronomical Union because he is funded by NASA, so that means he wasn’t eligible to receive the Edgar Wilson award when he found a comet last year.
Because of Holmes outstanding astronomical work, he is also an adjunct faculty member in the physics department at Eastern Illinois University in Charleston, Illinois.
[/caption]
When a star is still in the earliest stages of formation, it doesn’t have enough temperature in its core to ignite fusion of hydrogen and helium. Instead, the star shines with just the gravitational energy of its continue collapse. Astronomers call this pre-star a T Tauri star. This early stage lasts about 100 million years before nuclear fusion kicks in and it becomes a true star.
As you might know, stars start out as vast clouds of cold molecular hydrogen. Some event, like a nearby supernova, causes the cloud to collapse. As it collapses, the cloud fragments into separate pieces, each of which will eventually become a star. The first stage in a star’s life is as a protostar. This is where fresh material is still falling into the center of the collapsing cloud. After about 100,000 years or so, everything is collected, and the T Tauri star gets going.
T Tauri stars actually look quite similar to main sequence stars. Their surface temperatures are about the same as a star of a similar mass, but they’re more luminous because they have a larger diameter. But T Tauri stars get all their energy from the gravitational collapse of the material. They’re violent babies. There’s evidence that T Tauri stars are covered with active sunspots, and they produce extremely powerful stellar winds. Some of the brightness we see from here on Earth is the T Tauri star’s powerful stellar winds heating up a protoplanetary disk surrounding them.
Over 100 million years, these stars slowly collapse until the temperature and pressure at their core is sufficient to ignite stellar fusion. At this point, the star is converting hydrogen into helium at it’s core, and has become a main sequence star.
A star like our Sun will remain a main sequence star for about 12 billion years, as long as the fuel lasts in its core.
We have written many articles about stars here on Universe Today. Here’s an article about about two telescopes acting together to image a T Tauri star, and here’s an article about a T Tauri binary ejected from its system.
[/caption]
There are hundreds of billions of stars in the Milky Way alone; young and old, large and small, quiet and violent. But they all started out in the same way. Let’s take a look at thebirth of stars.
When we look out in the Milky Way, what we see are the stars, but a large part of the galaxy’s mass comes from clouds of molecular hydrogen; the stuff of future stars. These clouds are happy to drift along in the Milky Way for millions and even billions of years until some kind of event causes the cloud to collapse. It could be the collision between two clouds, or the shockwave of a passing supernova. This pushes the cloud over the top and gives gravity a chance to take over, and begin collapsing the cloud together.
As the cloud collapses, big pieces shear off. Each of these will become a star of their own. The mutual gravity on each chunk of the cloud continues to pull the material inward. The conservation of momentum from all the individual particles in the cloud makes it start to spin.
The first stage in the birth of a star is called a protostar. This is where the majority of the stellar material has collected together in ball in the center, but there is a huge disk of gas and dust obscuring it from our view. As long as there is still inflowing material, the object is a protostar. After enough material falls in on the star, jets of material blast out from either pole, announcing the new protostar to the Universe. The protostar stage takes about 100,000 years to complete.
Once there’s no more material falling inward, all that’s left is a hot ball of gas. Astronomers call this stage a T Tauri star. It doesn’t have internal temperature and pressure to begin nuclear fusion at its center, but it’s still a very hot object, and can appear as bright as a regular star. Over the next 100 million years, gravity continues to collapse the T Tauri star until the temperature at its core reaches the point that nuclear fusion can begin.
At this point, the star makes a transition to the main sequence stage of its life. This is a place it’ll remain for millions, billions, and even trillions of years depending on its mass.
[/caption]
Did you ever wonder what stars are made of? You might not be surprised to know that stars are made of the same stuff as the rest of the Universe: 73% hydrogen, 25% helium, and the last 2% is all the other elements. That’s it. Except for a few differences here and there, stars are made of pretty much the same stuff.
After the Big Bang, 13.7 billion years ago, the entire Universe was a hot dense sphere. The conditions inside this young Universe were so hot that it was equivalent to being inside the core of a star. In other words, the entire Universe was like a star. And for the brief time that the Universe was in this state, nuclear fusion reactions converted hydrogen into helium to the ratios we see today.
The Universe kept expanding and cooling down, and eventually the hydrogen and helium cooled down to the point that it could actually start collecting together with its mutual gravity. This is how the first stars were born. And just like the stars we have today, they were made up of roughly 73% hydrogen and 25% helium. These first stars were enormous and probably detonated as supernovae within a million years of forming. In their life, and in their death, these first stars created some of the heavier elements that we have here on Earth, like oxygen, carbon, gold and uranium.
Stars have been forming since the Universe began. In fact, astronomers calculate that 5 new stars form in the Milky Way every year. Some have more of the heavier elements left over from previous stars; these are metal-rich stars. Others have less of these elements; the metal-poor stars. But even so, the ratio of elements is still roughly the same. Our own Sun is an example of a metal rich star, with a higher than average amount of heavier elements inside it. And yet, the Sun’s ratios are very similar: 71% hydrogen, 27.1% helium, and then the rest as heavier elements, like oxygen, carbon, nitrogen, etc. Of course, the Sun has been converting hydrogen into helium in its core for 4.5 billion years.
Stars everywhere are made of the same stuff: 3/4 hydrogen and 1/4 helium. It’s the stuff left over from the formation of the Universe, and one of the most elegant pieces of evidence to help explain how we’re here today.
Eta Carinae Credit: Gemini Observatory artwork by Lynette Cook
[/caption]
Small stars release small amounts of energy, and huge stars release tremendous amounts of energy. Astronomers refer to the amount energy coming off the surface of a star as “luminosity”.
As a baseline, astronomers measure the luminosity of other stars against the power of the Sun. So here’s the luminosity of the Sun: 3.839 x 1026 watts, or 3.839 x 1033erg/s. When you use this number, you can calculate how much of that energy hits the Earth, or would be visible from a specific distance.
To be able to calculate the luminosity of a star, there are three variables at play: distance, apparent magnitude, and visible luminosity. If you have two of those variables, you can always calculate the third.
Let’s take a look at the smallest, least luminous stars out there: red dwarfs. A red dwarf can be as small as 7.5% the mass of the Sun, and up to 50% of the Sun’s mass. An average red dwarf has 1/10,000th the luminosity of our Sun.
Red giants, on the other hand, look cool and red, but you’ve got to remember that they’re huge. A typical red giant in our Solar System would engulf the orbit of the Earth. A red giant may be releasing 1,000-10,000 times the luminosity of the Sun. The largest known red giant is about 1,800 times larger than the diameter of the Sun. It emits about 430,000 times as much energy as the Sun.
The most energetic stars out there are the blue stars. A fairly familiar blue star is Rigel, located in the constellation Orion. Rigel has 17 times the mass of the Sun, is located about 800 light years away. Its surface temperature is at least 11,000 Kelvin. And this blue giant star is putting out about 40,000 times as much energy as the Sun.
But perhaps the most energetic stars in the Universe are the blue hypergiants. The best example is Eta Carinae. This monster is thought to have 150 times the mass of the Sun. It’s surface temperature is about 40,000 Kelvin, and it’s thought to be blasting out more than a million times the energy of the Sun.
Artist's impression of a red giant star. Image credit: ESO
[/caption]
You might be surprised to know that the color of stars depends on their temperature. The coolest stars will look red, while the hottest stars will appear blue. And what defines the temperature of a star? It all comes down to mass.
The most common stars in the Universe are the relatively tiny red dwarf stars. These stars can have as little as 7.5% the mass of the Sun, and top out at about 50%. Red dwarfs use their stores of hydrogen fuel very slowly; it’s believed that a red dwarf star with about 10% the mass of the Sun may live for 10 trillion years or more. Our own Sun will only live for about 12 billion years. Red dwarf stars have a surface temperature of less than 3,500 Kelvin, and this is why they appear red to our eyes.
Our own Sun is classified as a yellow dwarf star. It has a surface temperature of about 5,800 Kelvin. Because of this temperature, the bulk of the light we see streaming from the Sun is yellow/white. Our Sun has been in the main sequence phase of its life for 4.5 billion years, and it’s expected to last another 7 billion years or so.
The hottest stars are the blue stars. These start at temperatures of about 10,000 Kelvin, and the biggest, hottest blue supergiants can be more than 40,000 Kelvin. In fact, there’s so much energy coming off the surface of a blue star that many could actually be classified as ultraviolet stars, it’s just that our eyes can’t see that high into the spectrum.
Artist's impression of the first stars. Image credit: NASA/WMAP
[/caption]
Astronomers now know that the Big Bang occurred 13.7 billion years ago. For the first few hundred million years, the entire Universe was too hot any stars to form. But then the Universe cooled down to the point that gravity could start pulling together the raw hydrogen and helium into the first ever stars.
The basic elements on the Universe, hydrogen and helium and a few trace elements, we formed during the Big Bang. For a brief moment, the entire Universe was at the temperature and pressure that hydrogen could fuse into helium. This is why we see roughly the same ratios of hydrogen to helium, everywhere we look in the Universe: 73% hydrogen, 25% helium, and the rest are trace elements.
Astronomers think that this pure hydrogen/helium mix allowed the first stars to grow much more massive than stars can get today. It’s believed that they could have gathered together several hundred solar masses. The most massive star that can form today is thought to only be about 150 solar masses. After that point, extreme winds coming from the star prevent any additional material from falling in.
This first generation of stars, which astronomers call Population III stars, would have lived short violent lives. They probably lasted just a million years or so, and then detonated as supernovae. But in their lives, these Population III stars would have created heavier and heavier elements at their cores, and in their violent deaths, they would have created the even more exotic heavier elements, like gold and uranium. It’s possible that the first stars went through a few quick cycles, pulling in material, detonating and seeing the region with heavier elements. Eventually the first long-term stars would have gotten going, stars with the amount of heavier elements we see today.
None of the first stars have ever been observed directly. There have been a few hints through gravitational lensing; using a nearby galaxy’s gravity to focus the light from a more distant quasar. The next generation of space telescopes, like the James Webb Space Telescope might be able to push the observable Universe back to these first stars.
Size comparison between the Sun and VY Canis Majoris, which once held the title of the largest known star in the Universe. Credit: Wikipedia Commons/Oona Räisänen
The biggest stars in the Universe are the red supergiant stars. And we’re talking really, really big. The largest known red supergiant is thought to be VY Canis Majoris, measuring about 1800 times the size of the Sun. Imagine if the Sun extended out to the orbit of Saturn. Let’s take a look at where red supergiant stars come from.
Red supergiants are similar to red giants. They form when a star runs out of hydrogen fuel in their core, begins collapsing, and then outer shells of hydrogen around the core get hot enough to begin fusion. While a red giant might form when a star with the mass of our Sun runs out of fuel, a red supergiant occurs when a star with more than 10 solar masses begins this phase.
The five largest known supergiants in the galaxy are red supergiants: VY Canis Majoris, Mu Cephei, KW Sagitarii, V354 Cephei, and KY Cygni. Each of these stars has a radius larger than 1500 times the size of the Sun. In comparison, regular red giant is only 200 to 800 times the size of the Sun.
Red supergiant stars don’t last long; typically only a few hundred thousand years, maybe up to a million. Within this period, the core of the red supergiant continues to fuse heavier and heavier elements. This process stops when iron builds up in the core of the star. Iron is the equivalent of ash when it comes to nuclear fusion. The process of fusing iron actually requires more energy than it releases.
At this point, many red supergiants will detonate as Type II supernovae.
Betelgeuse was the first star directly imaged -- besides our own Sun, of course. Image obtained by the Hubble Space Telescope. Credit: Andrea Dupree (Harvard-Smithsonian CfA), Ronald Gilliland (STScI), NASA and ESA
When star like our Sun reaches the end of its life, it enters one last phase, ballooning up to many times its original size. Astronomers call these objects red giant star, and you’ll want to learn more about them, since this is the future fate for the Sun. Don’t panic, we’ve got another 7 billion years or so before the Sun becomes a red giant star.
As you probably know, stars shine because they’re converting hydrogen into helium in their cores through a process called nuclear fusion. Our own Sun has been performing fusion at its core for 4.5 billion years, and will continue to do so for another 7 billions years, at least. The helium byproduct from this fusion reaction slowly builds up in the core of a star, and they have no way to get rid of it. Eventually, billions of year down the road, a star uses up the last of its hydrogen fuel.
Once a star exhausts this fuel source, it no longer has the outward light pressure to counteract the gravity pulling in on itself. And so, the star begins to collapse. Before the star can collapse too far, though, this contraction heats up a shell of hydrogen around the core of the star to the point that it can support nuclear fusion. The higher temperatures lead to increasing reaction rates, and the star’s energy output increases by a factor of 1000 to 1000x. This new extreme light pressure pushes out the star’s outer layers beginning its life as a red giant star.
A red giant will expand outward many times its original size. Our own Sun, for example will grow so large that it engulfs the orbits of Mercury, Venus and even Earth; although, it’s not certain if Earth will actually be destroyed when this happens.
The core of the star will become so hot and dense that the leftover helium fuel will no able to star fusing into heavier elements. Stars with the mass of our Sun will stop with helium, but more massive stars will keep going, fusing carbon and even heavier elements together.
Without any more fuel to burn, these stars will expel their outer layers and then contract down to become white dwarfs.
We have written many articles about stars here on Universe Today. Here’s an article about a planet surviving when its star became a red giant. And were you wondering if the Earth will survive when the Sun becomes a red giant?
