Normal Galaxies & Starburst Galaxies
Nearly a million seconds of observing time with NASA's Chandra X-ray Observatory has revealed a spiral galaxy similar to the Milky Way glittering with hundreds of X-ray points of light.
The galaxy is officially named Messier 51 (M51) or NGC 5194, but often goes by its nickname of the "Whirlpool Galaxy." Like the Milky Way, the Whirlpool is a spiral galaxy with spectacular arms of stars and dust. M51 is located about 30 million light years from Earth, and its face-on orientation to Earth gives us a perspective that we can never get of our own spiral galactic home.
NASA's Chandra X-ray Observatory has shed new light on the mystery of why giant elliptical galaxies have few, if any, young stars. This new evidence highlights the important role that supermassive black holes play in the evolution of their host galaxies.
Because star-forming activity in many giant elliptical galaxies has shut down to very low levels, these galaxies mostly house long-lived stars with low masses and red optical colors. Astronomers have therefore called these galaxies "red and dead".
We are perhaps living in the midst of a new "Golden Age" of astronomy. In the four hundred years since Galileo first trained his refracting optical telescope on the Moon, and Jupiter and its moons, we've seen staggering advances in the technology of telescopes. We've also benefited from the discoveries of light beyond the visible portions of the electromagnetic spectrum and the development of instruments sensitive to those wavelengths.
We are very pleased to welcome Jay Strader as a guest blogger today. Jay is the first author of a paper describing evidence for the densest known galaxy in the nearby universe, the subject of our latest press release. He is an assistant professor in the Department of Physics and Astronomy at Michigan State University. From 2007-2012 he was a Hubble Fellow and Menzel Fellow at the Harvard-Smithsonian Center for Astrophysics. He earned his BS in Physics and Mathematics at Duke University, and his PhD at the University of California-Santa Cruz. As his Twitter biography says (@caprastro), he loves "goats, birds, the Celtics, and globular clusters".
Explaining the basic properties of galaxies from spirals like our own Milky Way to dwarf galaxies like the Magellanic Clouds has been one of the central occupations of astronomers over the last few decades. Most astronomers now favor a picture in which galaxies form at the center of condensed "halos" of mysterious dark matter. Gas flows into these halos, cools, and forms stars and planets. The most massive galaxies are built up by mergers of smaller galaxies, which can shut off new star formation and leave behind "dead" elliptical galaxies. This basic scenario is a framework through which we can understand the formation of the known types of galaxies.
Observations with NASA's Chandra X-ray Observatory have revealed a massive cloud of multimillion-degree gas in a galaxy about 60 million light years from Earth. The hot gas cloud is likely caused by a collision between a dwarf galaxy and a much larger galaxy called NGC 1232. If confirmed, this discovery would mark the first time such a collision has been detected only in X-rays, and could have implications for understanding how galaxies grow through similar collisions.
We are delighted to welcome Robin Barnard as a guest blogger today. Robin is currently a research fellow at the Harvard-Smithsonian Center for Astrophysics; originally from the UK, he has greatly enjoyed living in the US for 3 years. He got his PhD at the University of Birmingham, and a MPhys (Hons) in Physics with Astrophysics from the University of Manchester; thanks to a quirky convention, he has considerably more letters after his name than in it! He was previously employed as a research fellow at the Open University.
I came to the USA to hunt black holes. Not nearby ones (that might be a bit scary), but ones in the nearby spiral galaxy known as the Andromeda Galaxy, or M31. As Grant & Naylor pointed out in the BBC TV series Red Dwarf: the thing about black holes, their main defining feature, is that they’re black; and the thing about space, the basic space color, is it’s black. This makes lone black holes very hard to see! However, black holes that are able to snatch material from an orbiting companion star can release huge amounts of energy, mostly as X-ray radiation. Such systems are called X-ray binaries (XBs), and neutron star plus normal star XBs are also possible (and indeed are more common). In our Galaxy, black hole binary systems with low-mass companions go unnoticed for long periods of time, occasionally exhibiting huge outbursts in X-rays; for this reason, they are known as X-ray transients. The similarity between known black hole X-ray transients and other low-mass X-ray transients suggests that most low-mass X-ray transients contain black holes.
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