Normal Galaxies & Starburst Galaxies

Data from NASA's Chandra X-ray Observatory have been used to discover 26 black hole candidates in the Milky Way's galactic neighbor, Andromeda, as described in our latest press release. This is the largest number of possible black holes found in a galaxy outside of our own.

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.

Scientists have used Chandra to make a detailed study of an enormous cloud of hot gas enveloping two large, colliding galaxies. This unusually large reservoir of gas contains as much mass as 10 billion Suns, spans about 300,000 light years, and radiates at a temperature of more than 7 million degrees.

The spiral galaxy NGC 3627 is located about 30 million light years from Earth. This composite image includes X-ray data from NASA's Chandra X-ray Observatory (blue), infrared data from the Spitzer Space Telescope (red), and optical data from the Hubble Space Telescope and the Very Large Telescope (yellow). The inset shows the central region, which contains a bright X-ray source that is likely powered by material falling onto a supermassive black hole.

In this holiday season of home cooking and carefully-honed recipes, some astronomers are asking: what is the best mix of ingredients for stars to make the largest number of plump black holes?

They are tackling this problem by studying the number of black holes in galaxies with different compositions. One of these galaxies, the ring galaxy NGC 922, is seen in this composite image containing X-rays from NASA's Chandra X-ray Observatory (red) and optical data from the Hubble Space Telescope (appearing as pink, yellow and blue).

In writing a press release, a major goal is to present the truth, and nothing but the truth. However, it isn't practical to present the whole truth. For example, the paper associated with our press release last week was only six pages long, but contained 38 references to other papers, and each of these papers contain many more references. This is how research advances, building incrementally on previous work. Since we have limited space in a press release we cannot present the whole truth and we only include the information that we think is crucial for explaining the result and its significance.

This artist's illustration shows an enormous halo of hot gas (in blue) around the Milky Way galaxy. Also shown, to the lower left of the Milky Way, are the Small and Large Magellanic Clouds, two small neighboring galaxies (roll your mouse over the image for labels). The halo of gas is shown with a radius of about 300,000 light years, although it may extend significantly further.

Over fifty years ago, a supernova was discovered in M83, a spiral galaxy about 15 million light years from Earth. Astronomers have used NASA's Chandra X-ray Observatory to make the first detection of X-rays emitted by the debris from this explosion.

This image of the Pinwheel Galaxy, or also known as M101, combines data in the infrared, visible, ultraviolet and X-rays from four of NASA's space-based telescopes. This multi-spectral view shows that both young and old stars are evenly distributed along M101's tightly-wound spiral arms. Such composite images allow astronomers to see how features in one part of the spectrum match up with those seen in other parts. It is like seeing with a regular camera, an ultraviolet camera, night-vision goggles and X-ray vision, all at the same time.

A new study has shown that galaxies with the most powerful, active, supermassive black holes at their cores produce fewer stars than galaxies with less active black holes. Researchers compared infrared readings from the Hershel Space Observatory with X-rays streaming from the active central black holes in a survey of 65 galaxies, measured by NASA's Chandra X-ray Observatory.