Astronomers have observed a probable white dwarf orbiting a black hole at a distance of around a million kilometers:
The close-in stellar couple -- known as a binary -- is located in the globular cluster 47 Tucanae, a dense cluster of stars in our galaxy about 14,800 light years away from Earth. While astronomers have observed this binary for many years, it wasn't until 2015 that radio observations revealed the pair likely contains a black hole pulling material from a companion star called a white dwarf, a low-mass star that has exhausted most or all of its nuclear fuel.
New Chandra data of this system, known as X9, show that it changes in X-ray brightness in the same manner every 28 minutes, which is likely the length of time it takes the companion star to make one complete orbit around the black hole. Chandra data also shows evidence for large amounts of oxygen in the system a characteristic of white dwarfs. A strong case can, therefore, be made that that the companion star is a white dwarf, which would then be orbiting the black hole at only about 2.5 times the separation between Earth and the moon.
"This white dwarf is so close to the black hole that material is being pulled away from the star and dumped onto a disk of matter around the black hole before falling in," said Arash Bahramian, lead author with the University of Alberta (Canada) and MSU. "Luckily for this star, we don't think it will follow this path into oblivion, but instead will stay in orbit."
Found at Michigan State University.
The ultracompact nature of the black hole candidate X-ray binary 47 Tuc X9 (open, DOI: 10.1093/mnras/stx166) (DX)
Considering the measured orbital period (with other evidence of a white dwarf donor), and the lack of transitional millisecond pulsar features in the X-ray light curve, we suggest that this could be the first ultracompact black hole X-ray binary identified in our Galaxy
(Score: 0) by Anonymous Coward on Wednesday March 15 2017, @10:36PM
Or they are always "A long time ago; far, far away" because other data will rule them out if they are closer.