According to astronomers, 'when a massive star dies, a completely new black hole is born and every second a new black hole is born somewhere in the universe'.
But black holes themselves are invisible in nature. So far, scientists have only been able to detect stellar mass blackholes when they are acting on a companion.
Recently, scientists have identified a stellar-mass blackhole that is quite alone.
This discovery opens up possibilities for exploration related to black holes.
According to researchers, there are about 100 million black holes in our galaxy that have not yet been seen.
Its really an exciting one. From the very beginning, finding black holes has been a challenge for astronomers.
Because, black holes do not shine like stars. Any object with mass distorts the fabric of space-time, and the greater the mass, the greater the warp.
But the density of a black hole is so high that a space can be contained in it.
They are the most powerful space monsters in terms of gravitational force, that is, if light is passing through it, it automatically turns towards the mouth of the blackhole, gets absorbed in it.
Astronomers have indirectly found a few hundred of these ghostly blackholes by observing how they affect their surroundings.
They have identified about 20 small, stellar-mass black holes in our galaxy, watching them eat away at invisible companion stars.
As the black hole draws matter from its neighbor, the material forms a swirling, glowing accretion disk that gives a substantial indication of the black hole's presence.
After decades of searching, astronomers have finally found a distinct stellar-mass black hole.
Located about 5,200 light-years away toward the center of our galaxy, the yet-to-be-named rogue black hole weighs about seven times the mass of the Sun.
It is moving faster than almost all visible stars in its region, which gives an indication about how it is formed.
Scientists believe that when a massive star loses its energy and dies, the supernova explosion it experiences may be uneven.
"This black hole seems to have received a natal kick at birth, which sent it rapidly away," says Kailash Sahu, an astronomer at the Space Telescope Science Institute in Baltimore.
The team's conclusion have been sent to The Astrophysical Journal.
The team used two techniques to detect the black hole: gravitational lensing and astrometry.
The first works because when gravity alters space-time, it changes the path that light passes through.
When a celestial body passes very close to a farther star in the sky than our line of sight, the star's light is bent as it moves away from the nearest object.
If the bending foreground object is relatively small—eg, a planet, star, or black hole, rather than an entire galaxy or galaxy cluster—the process is, specifically, called microlensing.
Microlensing makes a near object act as a natural magnifying glass, temporarily brightening the light of a distant star – an effect binoculars can pick up.
Astronomers can roughly estimate how long a spike in starlight lasts; More massive objects create longer microlensing events.
Therefore, a prolonged microlensing event caused by something we cannot see could indicate the presence of a rogue black hole.
But black holes cannot be confirmed by microlensing alone.
A small, faint star slowly moving forward may turn out to be a black hole.
It will also produce a long signal due to its slow motion, and if the star is dim enough, astronomers cannot see it, only being able to detect light from the background star.
This is where astrometry comes in. This technique involves making precise measurements of the position of an object.
By observing how much the position of the background star changes during a microlensing event, astronomers can gauge very precisely how large the nearest object is.
"That's how we found out we found a black hole," says Sahu. "The object we have detected is so massive that if it were a star, it would be as bright as the Sun; yet we did not receive any light from it".
The discovery is the culmination of nearly seven years of observations. Microlensing signals that can reveal small, single black holes last about a year.
Two ground-based telescopes, the Optical Gravitational Lensing Experiment (OGLE) and the Microlensing Observation in Astrophysics (MOA) telescope, picked up on the event.
This went on long enough that astronomers suspected that the lensing object might be a black hole. That's when he started making astrometric measurements.
The deflection of the interfering object in the light of the background star was so small that only the Hubble Space Telescope could gather information about it.
The team spent several more years analyzing the astrometric signal that can normally last five to 10 times longer than its microlensing counterpart.
"It's a great pleasure to be a part of such a great discovery," Sahu Says. "I've been searching for rogue black holes for over a decade, and it's so exciting to finally find one! I hope this is the first one yet"
It is still possible that the object is not a black hole. A different team's analysis of the same event puts the object between about 1.5 and 4 solar masses – so light that it could be either a black hole or a (the crushed core of a dead star that is quite massive).
Given that astronomers have never detected an isolated neutron star before, this would still be a remarkable discovery.
The findings of both teams are still being reviewed.
Despite this result, some astronomers think that stellar-mass black holes found in binary systems may represent a biased sample.
Their mass only ranges from about 5 to 20 times the mass of the Sun, with most weighing around 7 solar masses. But the actual range can be quite wide.
"Stellar-mass black holes detected in other galaxies via gravitational waves are often far larger than the black holes found in our own galaxy - up to about 100 solar masses," says Sahu.
"The more that are isolated, the better we'll be able to understand what real black hole populations are like and learn even more about the ghosts that haunt our galaxy."
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