Hubble Burning Questions
From HubbleCast and the incomparable Dr. J. The episode features answers to questions submitted by the public. What is the most empty spot of space you have ever seen? What’s the longest single-shot exposure ever recorded of any object or area of space by Hubble? What are the farthest objects discovered by Hubble?
Three questions, just one answer. In 2003, Hubble was pointed at a part of sky which is, by normal standards at least, pretty empty. In particular, there are no bright stars in this area.
Now Hubble observed this field, which is only about a tenth the size of the full moon, for almost a million seconds. That’s around 11.3 days’ worth of total exposure time. The result is an image we call the Hubble Ultra Deep Field, and it is in fact the deepest optical image of the Universe that humanity has ever produced.
This is galaxy UDFj-39546284. Boring name, I know, but the point is that this is probably the most distant object ever discovered. Now its distance isn’t 100% confirmed yet, but it’s believed to be so far away that the light took 13.2 billion years to reach us. That’s about 96% of the age of the Universe.
When galaxies collide and incorporate each other, what happens to the black holes? Do they eventually merge into one giant black hole? Yup, that’s pretty much what happens.
As Hubble helped us discover in the 1990s, we think that almost all massive galaxies contain a central, supermassive black hole.
In addition, galaxy collisions are very common: they happen all the time and again, Hubble has showed us lots of great images of these collisions.
Now, eventually the two galaxies merge and settle into a single bigger new galaxy, and during this process, the same thing happens with their supermassive black holes. They merge into a single, even bigger, supermassive black hole at the centre of the new galaxy.
Now astronomers have made computer simulations of how this process works, but we also have some pretty good observational evi