- There may be an entire class of black holes that we didn’t know about.
- Astronomers have spotted a black hole that is smaller than the smallest known black holes in the universe.
- It is just 19 kilometers wide and has a mass of about 3.3 solar masses.
In theory, a black hole can weigh as little as 22 micrograms (the Planck mass). However, most of the black holes observed to date are billions of times more massive. For instance, the supermassive black holes at the centers of galaxies are the largest type of black holes, on the order of hundreds of thousands to billions of solar masses.
Until now, the smallest black holes astronomers knew about were all between about 5 and 15 times the mass of the Sun. It seems that things are about to change pretty soon.
A new study shows that there may be an entire class of black holes that we didn’t know about. These black holes could be several magnitudes smaller than the smallest known black holes in the universe.
Searching Black Holes In A New Way
For years, astronomers have been looking for black holes and neutron stars. Both celestial bodies reveal crucial information about the elements on Earth. To uncover such data, it’s important to determine where black holes are and what they look like.
What we already know that is low-mass black holes often exist in binary star systems (two stars orbiting each other). When one of those stars runs out of its fuel, it either turns into a neutron star or black hole.
Usually, neutron stars have a mass of up to 2.1 solar masses. If they were more than 2.5 times the mass of the sun, they would collapse into a black hole.
The team gathered light spectra from 100,000 stars across the Milky Way using data from Apache Point Observatory Galactic Evolution Experiment (APOGEE). This data helped them find stars orbiting around another celestial body (an unseen companion).
Researchers carefully analyzed the data and narrowed it to 200 stars that might be orbiting a black hole. They then used the All-Sky Automated Survey Supernovae (ASAS-SN) to compile thousands of pictures of each potential binary system.
Surprisingly, they stumbled upon an interesting binary system (J05215658) – a giant red star appeared to be orbiting a mysterious object. The calculations showed that this mysterious object is nothing but a small black hole. It is way smaller than currently known smallest black holes in the universe but larger than most neutron stars.
Additional data and evaluations from the Gaia satellite and the Tillinghast Reflector Echelle Spectrograph confirmed that it is a low-mass black hole, approximately 3.3 times the mass of the sun.
How Small Is It and Why Does It Matter?
The black hole is just 19 kilometers wide. It situated 10,000 light-years away, in the outer edge of our galaxy’s main disk. Further studies are needed to confirm its existence. If confirmed, this would be the smallest known black hole on record.
Further analyzes of this binary star system could help researchers extract more information about the black hole (such as its mass) and determine factors that affect the afterlife of stars.
In other words, if we could uncover a new class population of black holes, we would be able to tell (more accurately) which stars form neutron stars and which form black holes.