# How can black holes be sometimes so gaseous?

One of the most massive Supermassive Black Hole observed is the one at the centre of the galaxy NGC1600 with a mass of 17 billion suns. It would have a density of ∼0.01kg/m^3, or one part in 100,000 times the density of water, or 1% the density of earth atmosphere at sea level.

But if there is so much gas why isn't the bh shrinking and becoming more dense as gravity would pull everything together?

• What is your source for the density? – Sir Cumference Jun 25 '16 at 11:40
• Hossam Aly Astrophysics Ph.D – Marijn Jun 25 '16 at 11:44
• The density of a BH isn't really defined, or would be infinite since it's a point. A BH has already shrunk as much as it possibly can. If you wish you can calculate its mass divided by the volume inside its Schwarzschild radius. For M = 17e6, this gives 64 g/cm³. – pela Jun 25 '16 at 12:06
• radius = 2MG/c^2 hyperphysics.phy-astr.gsu.edu/hbase/astro/blkhol.html The big ones get positively ethereal, density-wise, calculating from the Schwarzschild radius. – Wayfaring Stranger Jun 25 '16 at 12:58