Podcaster: Morgan Rehnberg
Title: Monthly News Roundup – The Disappearing Act
Link : http://cosmicchatter.org
Black holes: http://astronomy.com/news/2014/02/rxte-reveals-the-cloudy-cores-of-active-galaxies
Description: In this episode of the Monthly News Roundup, an asteroid goes missing and we zoom in on an ancient galaxy. MESSENGER snaps its 200,00th image and MRO takes a nifty one, too. A NASA telescope lends insight into the world of black holes.
Bio: Morgan Rehnberg is a graduate student in astrophysics and planetary science at the University of Colorado – Boulder. When not studying the rings of Saturn, he develops software to help search for asteroids that might hit the Earth. He blogs and podcasts about astronomy and space science at http://cosmicchatter.org.
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You’re listening to the 365 Days of Astronomy podcast for February 27th, 2014. I’m Morgan Rehnberg, here with Vivienne Baldassare, and this is the Monthly News Roundup. This episode was produced February 24th in Boulder, Colorado.
Our top story this month is the case of a disappearing asteroid. Asteroid 2000 EM26 was supposed to cruise by Earth at the comfortable distance of three and a half million kilometers back on February 17th. Astronomers used the ground-based Slooh Space Camera to try and catch a view as it passed by. The result? Nothing. The asteroid was nowhere to be found.
How could a nearly three hundred meter hunk of rock just disappear? It’s not as far-fetched as you might think. As its name implies, asteroid 2000 EM26 was first observed back in the year 2000. In fact, it was only ever observed in the year 2000, and then only for nine days. Such a short period of observation makes it difficult to precisely chart the orbit of the asteroid; over the next 14 years, errors in the initial calculation were compounded by time. In fact, some have suggested that its true position actually differs by more than one hundred degrees.
Fortunately for us, 2000 EM26 poses no threat to the Earth. But, in the future, how can we stop more incidents like this? The answer is pretty simple: we need more regular observation of asteroids that might come near us. We can do this, but it’ll cost us and NASA is already stretched pretty thin. So, more realistically, we’ll continue to rely on the face that the Earth is a pretty small target surrounded by a whole lot of empty space. The odds are on our side.
Astronomers have identified one of the most distant galaxies ever observed, over 13 billion light years away. This means we are seeing the galaxy as it was just 650 million years after the Big Bang. Galaxies this far away are ordinarily too faint for our telescopes to observe. But this distant galaxy, known as Abell 2744_Y1, had the good fortune to be located behind a giant galaxy cluster.
Einstein was the first to predict that rays of light could be bent and magnified by the gravity of an object sitting between the light source and the observer. This idea was later extrapolated by astronomer Fritz Zwicky, who predicted that galaxy clusters, which are extraordinarily massive, could bend and magnify the light of galaxies behind them. When the alignment is just right, the background galaxies are stretched out into arcs of light surrounding the galaxy cluster. This phenomenon is known as gravitational lensing.
Abell 2744_Y1 is one such gravitationally lensed object. The galaxy cluster Abell 2744 sits between us and this distant galaxy, and when light from the background galaxy reaches the cluster, it is both bent and magnified. This enables astronomers to see the distant background galaxy; without gravitational lensing, it would be too faint for us to find.
Being able to see these distant galaxies is incredibly valuable for astronomers. By studying how big they were, how fast they were forming stars, and what their black holes were like, we can learn about how they evolved over cosmic time into the galaxies we see today. This particular galaxy turns out to be one thirtieth the size of the Milky Way, but is forming ten times as many stars!
This galaxy was discovered as part of the Hubble Space Telescope Frontier Fields project, which has dedicated a significant amount of observing time to image six large galaxy clusters. We’ll likely find more distant galaxies such as this as the project continues.
Gazing upon the cratered surfaces of solar system objects like the Moon, Mercury, and Mars, it’s hard not to think of them as having existed forever. After all, surely the forces that could produce such tortured terrain must be long gone. In a sense, it’s true – many of these surfaces are billions of years old. And, certainly, the sorts of events which produced the continent-sized impacts still visible to this day are a distant memory. But that doesn’t mean the surfaces of the planets, moons, and asteroids in the solar system are no longer changing!
We got a big reminder of that this month, with the discovery of a brand-new crater. In nearly eight years in orbit, NASA’s Mars Reconnaissance Orbiter has returned hundreds of thousands of stunning pictures of the surface of Mars. In that span, it has observed some regions many times. This allows it to record changing surface processes. On November 19th of last year, acting on an observation from back in 2012, it snapped an image of a brand new 30-meter crater on the surface of Mars!
Now, a new crater on the surface of Mars isn’t too surprising – after all, hundred of objects strike Mars every year. But this one is unusually large, making it easy to pick out from orbit. So when did the impact occur? Sometime between July 2010 and May 2012 – the interval between images of this region.
Discovering a young crater like this is quite valuable. Planetary scientists and geologists can now watch how the Martian weather affects it in near real-time. And this isn’t just interesting for its own sake: the age of every surface in the solar system is determined by the craters embedded in it.
In order to find the precise age of a surface, we need to pick up some of its rocks, take them back to a laboratory, and measure the ratios of certain elements found within. We’ve done this for only one body – the Moon, using lunar rocks returned by the Apollo astronauts. For every other surface in the solar system, we make a simple assumption: that craters build up around the solar system at about the same rate everywhere. Thus, an area with about as many craters as a similar region on the Moon likely has a commensurate age. So, understanding how craters degrade could have a very real impact (no pun intended!) on the ages of objects everywhere!
We now have a better idea of what the regions around active supermassive black holes look like, thanks to data collected over 16 years by NASA’s Rossi X-ray Timing Explorer. This space telescope specialized in measuring very short variations in the x-ray signal coming from an object. It was able to detect changes occurring on timescales less than one ten-thousandth of a second. This capability was essential for studying the x-ray signals coming from pulsars, or incredibly dense dead stars that spin hundreds of times a second. RXTE ceased operations two years ago, but astronomers continue to analyze the data it collected
A team of astronomers recently used data from RXTE to study variations in the signals coming from galaxies with active black holes. As material falls into a black hole, it speeds up and gets hotter. This can produce lots of high-energy X-rays. When astronomers looked at the X-ray signals coming from the centers of these galaxies, they noticed that the signal would sometimes disappear for days, or even years at a time. The astronomers concluded that this was due to very dense clouds of gas and dust passing between us and the black hole, and blocking the X-ray signal from reaching us. The bigger the cloud, the longer the X-rays disappear for. These clouds can be up to 0.25 light days across, or about 6 billion kilometers. That’s approximately the distance between the Sun and Pluto. While astronomers knew that disks of gas and dust orbit around black holes, this is the first confirmation that these disks are clumpy and contain clouds capable of obscuring X-ray emission.
Astronomers have been monitoring a gas cloud called G2 that is orbiting the supermassive black hole at the center of our Milky Way. We expect it to reach its point of closest approach to the black hole this year. If the gas cloud gets close enough to be torn apart, some may fall into the black hole – if this happens, we may see variation in the X-ray emission coming from the center of our own galaxy!
We end this month with congratulations for the MESSENGER team. Less than three years after entering orbit around Mercury, MESSENGER has returned more than two hundred thousand images of the innermost planet. That’s more than one hundred times more than they hoped to capture.
Launched in 2004 and arriving at Mercury in 2011, MESSENGER has revolutionized our understanding of the planet. Carrying a payload which includes imagers, spectrometers, and a laser altimeter, MESSENGER has produced maps of Mercury’s surface, atmosphere, and chemical composition.
Given the remarkable wealth of information returned, it’s hard to remember a time before MESSENGER. But, in the years leading up to the mission, we knew as little about Mercury as we do today about Pluto. To me, it’s a stark reminder that even the shortest distances can represent nearly insurmountable barriers in space. When we finally overcome these barriers, it’s great to see us making full use of the opportunity.
Thanks for listening to this episode of the Monthly News Roundup. For more astronomy news and commentary, visit http://cosmicchatter.org or follow @cosmic_chatter on Twitter. As always, you can contact us with your comments and corrections at firstname.lastname@example.org. See you in March!
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