Why don’t planet hunters find black holes?

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SUMMARY

The discussion centers on the challenges of detecting black holes compared to the discovery of over 200 exoplanets using the radial velocity technique. Participants highlight that systems with a star orbiting a black hole typically become X-ray binaries, where matter is drawn into an accretion disc, emitting X-rays. The periodic Doppler shifts of stellar spectral lines in these systems are significant, yet black holes are less common than planets, making their detection more complex. The example of V4641 Sgr, located 1600 light years away, illustrates the distance at which black holes can be found.

PREREQUISITES
  • Understanding of radial velocity technique in exoplanet detection
  • Knowledge of X-ray binaries and their characteristics
  • Familiarity with Doppler shifts and their implications in astrophysics
  • Awareness of accretion discs and their role in black hole systems
NEXT STEPS
  • Research the methods used to detect X-ray binaries
  • Study the properties and formation of accretion discs around black holes
  • Explore the significance of Doppler shifts in astrophysical observations
  • Investigate the distribution and frequency of black holes in the universe
USEFUL FOR

Astronomers, astrophysicists, and students interested in exoplanet detection and the study of black holes will benefit from this discussion.

jimgraber
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Over 200 planets have been discovered by the radial velocity technique. Why no black holes? For similar periods, the signal amplitude should be much greater.
TIA.
Jim Graber
 
Astronomy news on Phys.org
I'm no expert in this area, but I believe that such systems (a star orbiting a black hole) would inevitably become what are known as "X-ray binaries", as matter is drawn from the star into a hot X-ray-emitting accretion disc around the black hole. The stellar spectral lines in such systems are indeed subject to enormous periodic Doppler shifts. I'm not sure how X-ray binaries are normally discovered though...
 
BHs are not nearly as common as planets
while they would really bounce a star's orbit
just looking for X-rays is a more common way to find them

V4641 Sgr is 1600 light years away at the closest found
 

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