How scientist find Black holes?

Black Hole 
Using the Event Horizon Telescope, scientists obtained a picture of the region at the middle of galaxy M87, outlined
by emission from hot gas swirling around it under the influence of strong gravity near its event horizon.

What are the smallest known black holes? Black holes are notoriously difficult for scientists to
find. This is because, unlike stars, light that falls within a black hole’s event horizon will never be seen. However, sometimes a
black hole has an accretion disk — a halo of material around the black hole that glows as it violently grinds together. The light
emitted from such accretion disks makes it possible for scientists to find these otherwise invisible objects. Astronomers also
spot black holes by noticing how they affect other objects, includingstars.For instance, scientists discovered Sagittarius A*
after spottingthe odd behavior of seven stars orbiting it. With these methods, scientists have found many black hole
candidates over the years, includingthe smallest known black hole located in a binarysystem called GRO J1655-40. The visible
companion star in this system is dumpinggas onto the black hole,generating enough energy to power a microquasar.
Quasars develop in extremely luminous active galactic nuclei, which are the centers of galaxies hosting a supermassive region
that's surrounded by a bright and energetic accretion disk. The black hole in GRO J1655-40 is estimated to weigh about 5.4
times the mass of the Sun, which would give it a radius of about 10 miles. By studying microquasars such as this, astronomers
hope to better understand the possible link between the monsters lurking in galactic cores and smaller, accreting black holes
spread throughout galaxies. In 2008, scientists believed they had found an even smaller black hole, but the mass was later
corrected bythe same team. Any smaller black holes would likely be due to the merger of two neutron stars rather than the
collapse of a dying star. The Laser Interferometer Gravitational-Wave Observatory detected gravitational waves from a
possible neutron star merger in 2017, just two years after detecting gravitational waves for the first time. Gravitational waves
emitted during mergers provide a new wayfor scientists to identify black holes within 100 million light-years of Earth. On the
other end of the spectrum, the size of a stellar-mass black hole depends on how massive the original star was. The most
massive star found to date is R136a1 and weighs in at 315 times the mass of the Sun. If it stayed at its current mass, the
resulting black hole from its inevitable collapse would have a radius of some 578 miles. Although large compared to the
smallest known black holes, even this heftystellar-mass black hole pales in comparison to its supermassive cousins.

Comments