| Illustration Credit: FECYT, IAC |
Astronomers believe there could be 100 million Black hole Among the stars of the Milky Way galaxy alone. Despite the existence of many theoretical black holes, it has been a struggle for scientists to identify an isolated black hole. Finally, after six years of ‘fine observation’, NASA’s Hubble Space TelescopePhantom has provided direct evidence of a single black hole flowing through interstellar space through precise mass measurements of objects.‘It was a big milestone, as before, the mass of all black holes Statistically estimated Or ‘through interactions in the binary system or in the core of the galaxy.’ Black holes of stellar mass are usually found with companion stars, which make the observed isolated black holes a special case.
The detected black hole is about 5,000 light-years away, orbiting the Carina-Sagittarius spiral arm of the Milky Way galaxy. The discovery of this distant black hole allows astronomers to speculate that there may be a black hole of isolated stellar mass very close to Earth, probably only 80 light-years away. For reference, the nearest star to our solar system, Proxima Centauri, is just over 4 light-years away.
Black holes scattered across our galaxy are formed when ‘rare, monstrous’ stars explode into supernovae at least 20 times larger than our Sun, crushing the remaining core by gravity into a black hole. Less than a thousandth of the stars in the galaxy are large enough to make it. Self-detonation is not perfectly symmetrical, so a black hole could be shot in a different direction, ‘taking care of it like a cannonball exploding through our galaxy.’
We know that there are millions of possible black holes in our galaxy, but they are challenging to observe. The primary reason is that they do not emit any light. However, for the same reason a black hole does not emit light – its extremely strong gravitational field does not allow light to escape – we can see evidence of a black hole how it scatters space and deflects and emits starlight from any star. Line up just behind it relative to the observation point. Simply put, scientists can detect black holes because they affect the objects around the black hole.
Ground-based telescopes are constantly orbiting the night sky, observing the brightness of millions of stars towards the central bulge of our Milky Way. When an observation shows that a star shows sudden brightness when a huge object passes through a telescope and a star, Hubble follows for further investigation.
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| In this Hubble Space Telescope photo, the starry sky is located towards the galactic center. The brightness of stars is observed to see if there is any change in the apparent brightness by a foreground object flowing in front of them. The scattering of space by interlocking due to an effect called gravitational lensing will brighten the appearance of a background star for a moment. One such incident is shown below along four close-up frames. The arrow points to a star that glows for a moment, as it was first captured by Hubble in August 2011. This was due to a foreground black hole flowing in front of the star along our line of sight. The star becomes brighter and then returns to its normal brightness as it passes through the black hole. Because a black hole does not emit or reflect light, it cannot be observed directly. But its unique thumbprint on space cloth can be measured through these so-called microlensing events. While an estimated 100 million isolated black holes are orbiting in our galaxy, a needle-in-a-haystack search for Hubble astronomers who have found one’s tailtail signature. ‘
Credit: NASA, ESA, and Kailash Sahu (STScI); Image processing: Joseph Dipasquel (STScI) |
Both teams used Hubble data for their investigations, including One Led by Kailash Sahu of the Space Telescope Science Institute in Baltimore, MD. The other Team Led by Casey Lam of the University of California, Berkeley. The two groups came up with slightly different results, but the research of each group indicated the presence of ‘a compact object’.
NASA writes, ‘The scattering of space due to the gravity of a foreground object passing in front of a star far behind will momentarily bend and widen its light as it passes in front of the background star. Astronomers use the phenomenon called gravitational microlensing to study stars and exoplanets in about 30,000 events seen so far inside our galaxy. ‘
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| ‘This illustrates how the gravity of a black hole scatters space and bends the light of a distant star behind it. A black hole is the crushed remnant of a giant star that exploded as a supernova. Black holes block light due to their intense gravitational field, so it cannot be seen directly. A black hole distorts the space around it, distorting images of stars almost directly aligned behind it. This proves the existence of a single black hole orbiting in our galaxy. The light of a background star is distracted and brightened by the intense gravitational field of the black hole. The Hubble Space Telescope detects these black holes as black holes flow in front of the background stars, distorting the light from the stars.
Credits: NASA, ESA, STScI, Joseph Olmsted |
A foreground black hole differs from other microlensing events because the gravity of a black hole can extend the duration of a lensing event by more than 200 days. Further, if the cause of the microlensing event is a star, it will cause a color change – no such transient color change occurs in a black hole event.
‘Then, Hubble was used by black holes to measure the deviation of the background star image.’ Hubble detected significantly more precise and offsets of about one millisecond. It’s like living in New York and measuring the diameter of a quarter of a coin in Los Angeles.
The astrometric microlensing technique provides information about the mass, distance and velocity of black holes. Sahu’s team used the amount of deviations caused by the space disaster of the black hole, that the weight of the black hole is about seven solar masses. Lam’s team reported a slightly lower mass range of about 1.6 to 4.4 times the mass of the Sun, meaning that the invisible object could be a neutron star instead of a black hole. If the mass is at the upper end of the range, it is a black hole. Otherwise, it is a neutron star.
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| ‘This is a close-up view of a black hole flowing through our Milky Way galaxy. A black hole is the crushed remnant of a giant star that exploded as a supernova. The surviving core is several times the mass of our sun. Black holes block light due to their intense gravitational field. A black hole distorts the space around it, distorting images of background stars almost aligned directly behind it. This gravitational “lensing” effect is the only evidence of the existence of a single black hole orbiting our galaxy, which could have a population of 100 million. The Hubble Space Telescope traces these black holes by looking for distortions in the starlight as black holes flow in front of the background stars.
Illustration Credit: FECYT, IAC |
‘As far as we’re concerned, this is definitely a black hole, we must report all approved solutions. That includes both a low-mass black hole and possibly a neutron star, “said Jessica Lu of the Berkeley team. Lam added, “Anyway, the object is the first dark stellar remnant to be discovered orbiting through the galaxy, with no other star companions.”
The source star has a bright, unrelated star at an angular resolution, which makes the measurement very challenging. ‘So it’s like trying to measure the small speed of a firefly next to a bright light bulb,’ Sahu said. “We had to very carefully subtract light from nearby bright stars in order to accurately measure the deviation of the faint source.” Sahu’s team estimates that isolated black holes travel across the galaxy at speeds of about 160,000 kph (100,000 mph). If so, it could land on the moon in less than three hours. If the speed measurements are accurate, black holes are traveling faster in that region of the galaxy than neighboring stars.
‘Astrometric microlensing is conceptually simple but very difficult to observe,’ Sahu said. “Microlensing is the only technique to detect isolated black holes.” The microlensing event lasted about 270 days, but it took several more years of Hubble observations to follow up on how the position of the background stars seemed to be ‘deviated by the bending of light by the foreground black hole’.
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| ‘This time-lapse uses four Hubble Space Telescope photos that capture the gravitational effects of an invisible black hole flowing through our galaxy. Because a black hole does not emit or reflect light, it cannot be observed directly. But its unique thumbprint on the space fabric can be measured in the way it distorts the light of a background star, an effect called gravitational microlensing. The background star became brighter for the moment, as Hubble began on August 1, 2011, and then returned to normal brightness as the foreground black hole floated away. A needle-in-a-haystack search for Hubble astronomers who found the conversation signature of an isolated black hole. ‘
Credit: NASA, ESA, and Kailash Sahu (STScI); Animation: Joseph Dipasquel (STScI) |
Other measured stellar-mass black holes in the binary star system have been measured by X-ray measurements. NASA writes, ‘Gas from a fellow star falls into a black hole and is heated to such a high temperature that it emits X-rays. Nearly two dozen black holes have measured their mass in X-ray binary through their gravitational effects on their mates. Mass estimates range from 5 to 20 solar masses. Black holes in other galaxies have been detected by gravitational waves from the merging of black holes and companion objects, like 90 solar masses.
‘Detecting isolated black holes will provide new insights into the population of this object in our Milky Way,’ Sahu said. However, it is believed that out of hundreds of microlensing events, only one is the result of an isolated black hole, which means at least it is a challenging search. NASA’s upcoming Nancy Grace Roman Space Telescope will observe ‘thousands of microlensing events’, many of which are expected to be due to black holes. The telescope will be able to measure the deviation with extreme accuracy.
