Researchers find 26 possible black holes in Andromeda , a galaxy near our own . Black holes ca n't be seen directly . It 's hard for scientists to distinguish distant black holes from neutron stars , however . They are hidden by the gravity of their host galaxies and so can only be detected indirectly through gravitational waves ( ripples ) emitted from them as they pass close to us.
Researchers find 26 possible black holes in Andromeda , a galaxy near our own . Black holes ca n't be seen directly . They are hidden by the gravity of their host galaxies and so can only be detected indirectly through gravitational waves ( ripples ) emitted from them as they pass close to us.