On a cosmic scale the notion of distance is more subtle than you might think.
Across the Universe
Just how far is the most distant galaxy known? That depends on what you mean by distance.
Quintet
In 1877 Édouard Stephan discovered a cluster of five galaxies in the constellation Pegasus. It came to be known as Stephan’s Quintet. The quintet is probably most famous for its use in the opening scene of It’s A Wonderful Life, so it is likely the best known galaxy cluster.
A Galaxy Far, Far Away
A while back in Nature a paper was published on the most distant confirmed galaxy discovered so far. The paper is behind a paywall, but you can see the arxiv version here. The galaxy, known as z8 GND 5296 has a measured redshift of 7.51. You can see the galaxy in the image above. So just how far away is this galaxy? It depends on which distance you are talking about.
Closer Than They Appear
Yesterday I talked about apparent sizes, and how Pluto can appear larger than a distant galaxy, even though the galaxy is much farther away. It turns out, however, that on really cosmic scales apparent size is only part of the story. That’s because the universe is expanding.
Seeing Red
Ever since Henrietta Leavitt discovered the period-luminosity relation for Cepheid variable stars, and Edwin Hubble used her work to demonstrate the relation between the redshifts of galaxies and their distances, we’ve had a pretty good idea that the universe was expanding. Since then we’ve gathered much more evidence on the connection between redshift and cosmic expansion, including redshift observations of distant supernovae that show the universe is undergoing cosmic inflation due to dark energy. While cosmic expansion is now well established, there have been some interesting mysteries along the way. One of these involves some seemingly strange behavior of quasars.
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.
Primeval Atom
The origin of the universe is often portrayed in popular science as a vast sea of darkness. Centered in this darkness is a bright point of light, which suddenly expands, filling your view with light, fading into a dance of galaxies. Of course this raises all sorts of questions: What did the universe expand into? What triggered the initial explosion? Where did all that matter and energy come from? The problem is, this isn’t how cosmologists see the big bang at all.
Dusty Starburst
A starburst galaxy is a galaxy that’s producing stars at a very high rate. The rate of star production is so high that it would use up the available gas and dust in a time period much shorter than the typical age of a galaxy. We often see starburst galaxies in the midst of a merger or close encounter with other galaxies, which would indicate that starburst periods can be triggered by galactic collisions.
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