8 kpc – The approximate distance of the Sun from the centre of our Galaxy
Our sun is one of a hundred billion or so stars in the Milky Way, travelling in relative peace in the outskirts of our home galaxy. About 8 kiloparsec (26 thousand light years) from us in the constellation Sagittarius lies the center of the Milky Way. It can be difficult to see all the way to the center due to the enormous amounts of gas and dust in the way, but astronomers have managed to pierce this veil to study the heart of the Milky Way galaxy.
Two teams of astronomers, one based in Germany at the Max Planck Institute for extraterrestrial Physics (great name!) and the University of California Los Angeles tracked the motion of stars using state of the art infrared cameras in the very heart of the Milky Way and found something remarkable. The stars in the center of our galaxy all orbit the same empty spot.
It was as if there were some great mass in the center and the stars all orbited it. When they calculated the mass of this dark object, it came back as four *million* times the mass of the sun. The only object so small, yet so massive, is a black hole. So next time you see Sagittarius in the night sky, think of the monster lurking there.
We now know that almost all galaxies contain such a supermassive black hole in the center, and the true monsters can be much more massive: up to ten billion solar masses in the centers of the most massive galaxies. When these black holes feast on gas and dust, they can light up as active galactic nuclei or quasars.
The Galaxy Zoo team has been working hard to understand the connection between galaxies and their black holes for the last 8 years, and we’ve learned a lot! Hanny’s Voorwerp has told us much about what black holes are really up to, and your classifications for so many SDSS galaxies has really helped us to understand this “co-evolution” better!
In the case of the Milky Way, we can see the echoes of recent outbursts of feeding from our black hole, from light echoes travelling across molecular clouds in the center, to the enigmatic Fermi bubbles, which many astronomers suspect are the aftermath of a powerful burst of accretion by our black hole.
All this, just 8 kiloparsec from our home solar system…. it’s really not that far away!