Year 12s: what will be the first way you research your future options? >>

black holes

I've been asked to give two reasons how we know black holes exist. I've got that we can detect the X-rays that are emitted but I don't know another reason. GCSE.

Reply 1

MeAndBubbles

they've modelled how the galaxies were formed, and each have super massive blackholes at the centre,

on tv i've watched astronomers infer one from the massive speed of stars in an area of space

Reply 2

Drummy

we can measure the rotational speed of galaxies (from red and blue shift) and knowing their radius we can work out their mass. The answers we gat tend to bigger than we expect suggesting that there must be "extra mass" somewhere in the galaxy we cant see.

It has been suggeted that this may take the form of dark matter and / or black holes.

Reply 3

F1 fanatic

gravitational lensing is the classic one you havent mentioned. Mass nends light, so that you see stars behind the black holes as smeared halos or auras around where the black hole is. The fact you can't see any mass indicates it is a black hole (or neutron star if its mass is low enough)

Reply 4

thelostchild

cant you also see accretion discs around them of matter being sucked into them and see how they distort stars around them, such as a star orbiting one?

Reply 5

F1 fanatic

thelostchild

cant you also see accretion discs around them of matter being sucked into them and see how they distort stars around them, such as a star orbiting one?

you mainly see the accretion disk by the x-ray radiation they emit, which is what was mentioned earlier. You can see star/black hole binaries, the difficulty there is in calculating the mass of the 2 stars to prove it is a black hole and not a neutron star. There aren't many none cases.