The image here is of the very center of the Andromeda galaxy. If you look in the middle of this image, you’ll see a smudge of blue. As first demonstrated in an article in Astrophysical Journal, the central blue region is a collection of about 400 young blue stars. They are concentrated in a region about a light year across, and are moving at about 1,000 km/s.
Hoag’s Object
Hoag’s object is perhaps the most famous example of a rare type of galaxy known as a ring galaxy. It is comprised of a core of older stars surrounded by a ring of young hot blue stars. When it was first discovered by Arthur Hoag in 1950, it was thought it might be an example of the gravitational lensing of a more distant galaxy by a closer one. Later observations showed that the ring and core have the same redshift, and so are of equal distance. More recent images such as the Hubble view seen here clearly indicate that the usual shape is not due to lensing. The galaxy really is shaped the way it looks. Just how it got that way is a bit of a mystery.
No Doughnut
Within most galaxies is a supermassive black hole. These black holes can have a mass of millions or even billions of Suns. When actively consuming material, these black holes can produce tremendous amounts of energy, and can be seen as quasars, blazars and radio galaxies, depending upon the way they are oriented relative to our vantage point. At least that’s been our understanding. But now a new paper in the Astrophysical Journal has thrown a wrench in one part of that idea.
Survey Says
The image below is the first complete x-ray survey of the Andromeda galaxy. The Andromeda galaxy (also known as M31) is about 2.5 million light years away. It is a spiral galaxy very similar to our own Milky way, so surveys of Andromeda are very useful in understanding galaxies like ours.
Selection Bias
There’s a new paper in the International Journal of Modern Physics which presents evidence that the universe is not expanding. You heard that right. If true it would overturn decades of cosmological theory. It’s the kind of revolutionary find that wins Nobel prizes. It’s gotten a bit of attention in the popular press, but don’t throw your old astronomy books out just yet.
It’s a Gas
Stars form within large clouds of gas and dust known as stellar nurseries. Of course, when a star forms, that leaves less gas and dust to form other stars. So you can do a bit of simple math concerning star formation. Take the rate at which new stars form in a galaxy (and their typical mass), compare that to the amount of gas and dust a galaxy has, and you can estimate the time over which stars can form.
Heart of Darkness
Star formation within a galaxy is a complex process. We have models of galaxy formation, but one of the difficulties with these models has been that they predict a greater formation of stars in large galaxies than we observe. This would seem to indicate that there is some mechanism that hinders star formation within large galaxies. Basically at some point in the galaxy’s formation there must be something that pushes gas out of the galaxy, preventing it from forming into stellar nurseries.
Reboot
One of the challenges faced by astrophysicists is that you can’t repeat your experiments. With cosmology, that poses a particular challenge because we only have one observable universe. Not only can’t we repeat the experiment, we only have one experiment to observe. What we can do, however, is simulate the universe and see how it compares to the real one.
Massive Speed
We now know that most galaxies have a supermassive black hole in their center. One of the ways to determine the mass is called reverberation mapping. By looking at variations in the brightness of active galactic nuclei, you can determine the size of the black hole. But we can only do this for about 40 galaxies, so it would be nice to have another way to determine black hole mass. It turns out there is, using a relation known as the M-sigma relation.