Astronomer tells Wikinews about discovery of closest black hole known so far
Friday, May 22, 2020
A study published in journal Astronomy & Astrophysics last month reported astronomers from the European Southern Observatory (ESO) and elsewhere discovered a black hole in the Telescopium constellation. The study stated the black hole is about 1010 ± 195 light years (310 ± 60 parsec) away from the Solar System, meaning it is the nearest known black hole from the Earth. The nearest previously known black hole — V616 Mon — the study noted was usually estimated at more than 3000 light years away.
The black hole described in the study is located in the HR 6819 stellar system of Telescopium constellation, making it the first system visible to the naked eye to contain a black hole. HR 6819 contains two stars, and they are visible from the Southern Hemisphere. The astronomers started observing the system in 1999. Initially, they thought it was just a binary system, consisting of two stars. However, upon examination, the researchers concluded there was a third unseen object in the system. One of the two stars in the HR 6819 system is close to the black hole and orbits the black hole in just 40.333 ± 0.004 days.
This newly discovered black hole does not have an accretion disk. A black hole forms an accretion disk when a significant amount of matter orbits the black hole, as depicted in the image. Accretion disks often emit electromagnetic radiation. Since this black hole does not have an accretion disk, researchers had to rely on the gravitational effect of the black hole on the nearby star in order to discover it.
Researchers used the binary mass function to conclude the black hole had a mass of at least 4.2 M? (Solar masses; 1 Solar mass = mass of the Sun). Its companion star, which orbits the black hole in about 40 days, is classified as a B3 III star. The outer star is classified as a Be star. Be stars rotate very quickly around their axes. Since the outer star rotates so rapidly, the star is not exactly spherical, but instead oblate, bulged at its equator, forming a gas disk around the equator.
The research suggested HR 6819 was very similar to another system LB-1. The HR 6819 system is estimated to be between 15–75 million years old (myr). The inner star has estimated mass of at least 6.3 ± 0.7 M?. Using the mass and the speed at which the inner star rotates, the researchers concluded the black hole had an estimated mass of 5.0 ± 0.4 M?. Researcher and co-author of the study Thomas Rivinius told Wikinews the inner star and the black hole are closer than the Sun and the Earth (1au; 150 million km; 93 million miles).
The researchers dedicated the paper to Stanislav Štefl, one of the fellow researchers who died in a car accident in 2014 in Santiago, Chile.
Wikinews caught up with Thomas Rivinius to discuss about this discovery.