Obviously you won’t see the Black Hole itself. A Black Hole is, well, black. It’s gravity is so intense that not even light can escape it. But I can point you to a couple of places where there almost certainly is a black hole.
Every large galaxy (probably) contains a supermassive black hole at its centre, including our own. So you just have to look at any galaxy in the sky and you’ll be looking at a black hole. Our own galaxy’s supermassive black hole is called Sagittarius A*. It has a mass over 4 million times the mass of the sun. If you’re familiar with the “Sagittarius Teapot” then it’s an easy find.
https://earthsky.org/favorite-star-patterns/teapot-of-sagittarius-points-to-galactic-center/
https://en.wikipedia.org/wiki/Sagittarius_A*
Unfortunately this is too low in the sky for me to see from my back garden. However, there are much closer black holes to earth, some of which are on our cosmic doorstep.
https://en.wikipedia.org/wiki/List_of_nearest_known_black_holes
The one I’m going to point out was the first confirmed, stellar mass, black hole. Lying 7,000 lights years from earth, it’s very easy to find in the night sky, especially right now.
We begin with our friend, the Summer Triangle. The three vertices of the triangle are the stars Deneb, Vega and Altair. They all lie due south at midnight at the moment and dominate the summer sky in the UK. The Milky Way, if you’re lucky enough to be able to see it, runs along the line connecting Deneb and Altair.
Deneb is the brightest star in the constellation of Cygnus, the Swan. This constellation also goes by the name of the Northern Cross, for obvious reasons when you see the picture below. Here’s a picture of the Summer Triangle and Northern Cross, taken with my Panasonic GF7 and a wide angle lens.
Follow the cross down from Deneb to Sadr, the centre of the cross. Then keep going to Eta Cygni. This is the star we’re interested in.
In the 1960s, when they first sent rockets equipped with X-Ray scanners above the earth’s atmosphere, it quickly became apparent that there was a very strong X ray source somewhere in the constellation of Cygnus. This was labelled as “Cygnus X ray source number one”, Or Cygnus X-1 for short. As better and better satellites did more refined observations, the source was narrowed down to near Eta Cygni. The actual star where they seemed to originate was very nearby. The star doesn’t have a name, just a catalogue number, HD 226868.
HD 226868 is a very massive, very hot star, about 30 times the mass of the sun. However, it’s not that hot that it should be emitting the kind of X rays that are observed from it. Studies of the star’s spectrum revealed a wobble due to a hidden, equally massive, companion. This hidden companion lies about the same distance from the star as earth is from Venus’ orbit. Almost everyone agrees that this hidden companion is a Black Hole. Even long term sceptic, Stephen Hawking, eventually conceded the point. The solar wind from HD 226868 provides just enough material to feed this hidden companion and let it generate the X rays that we see above the earth’s atmosphere.
Here’s a picture of HD 226868 taken with my Seestar S50. The bright yellow star on the right is Eta Cygni. For scale, the distance between the two stars in this picture is about half a degree in the sky, the width of the full moon. That may sound like a lot, but the full moon isn’t nearly as big as many people think it is. It only spans about a tenth of the angular distance between Eta Cygni and Sadr at the centre of the Northern Cross.
So next time you’re looking up at the sky, see if you can find Eta Cygni. When you do, you’re looking almost directly at a Black Hole.
Platitude of the Day 