What is the mystery behind disappearance of supermassive black hole

 "It’s there, it’s just being very hard to find."

A supermassive black hole, which is estimated to weigh up to 100 billion times the mass of the Sun, is seemingly missing, leaving astronomers baffled.

Nasa's Scientists have been looking for this supermassive black hole using Hubble Space Telescope but so far no evidence have been found till now.

Many social media users have expressed confusion about the black hole’s whereabouts, which is supposed to be at the center of a far-off galaxy.

In this blog we will come know about what is black hole, its history, mystery behind its disappearance and theories connected to it.

What is Black Hole?                                                            

Black hole, cosmic body of extremely intense gravity from which nothing not even light can escape. A black hole can be formed by the death of a massive star. When such a star gets exhausted the internal thermonuclear fuels in its core at the end of its life, the core becomes unstable and gravitationally collapses inward upon itself, and the star’s outer layers are blown away. The crushing weight of constituent matter falling in from all sides compresses the dying star to a point of zero volume and infinite density which is called the singularity.

Details of the structure of a black hole are calculated from Albert Einstein’s general theory of relativity. The singularity constitutes the center of a black hole and is hidden by the object’s “surface,” the event horizon. Inside the event horizon the escape velocity (i.e., the velocity required for matter to escape from the gravitational field of a cosmic object) exceeds the speed of light, so that not even rays of light can escape into space. The radius of the event horizon is called the Schwarzschild radius, after the German astronomer Karl Schwarzschild, who in 1916 predicted the existence of collapsed stellar bodies that emit no radiation. The size of the Schwarzschild radius is proportional to the mass of the collapsing star. For a black hole with a mass 10 times as great as that of the Sun, the radius would be 30 km (18.6 miles).

Some black holes apparently have non stellar origins. Various astronomers have speculated that large volumes of interstellar gas collect and collapse into supermassive black holes at the centers of quasars and galaxies. A mass of gas falling rapidly into a black hole is estimated to give off more than 100 times as much energy as is released by the identical amount of mass through nuclear fusion. Accordingly, the collapse of millions or billions of solar masses of interstellar gas under gravitational force into a large black hole would account for the enormous energy output of quasars and certain galactic systems.

History of Back Hole

In 1916 Schwarzschild read Einstein’s paper on general relativity. He was interested in the physics of stars, and had a lot of spare time between battles on the Russian front, so he solved

Einstein’s field equation for the region outside a massive spherical object. His solution had many interesting features, including

1. prediction of space warping in strong gravity, and invention of embedding diagrams to visualize it.

2. verification gravitational time dilation, just as Einstein had pictured it.

3. prediction of black holes, though this was not recognized at the time.

Schwarzschild’s solution

Describes the spacetime curvature near a massive, spherically

symmetric body. Solution ONLY depends on BH MASS.

As the radius of the object becomes smaller than a critical

value, the spacetime curvature becomes infinite

Evidence for this spin shows in how the black hole pulls everything around the horizon, essentially sweeping up space-time itself into a swirling vortex. This allows gas to move ever faster as it spirals closer and closer to the horizon, leading to more extreme Doppler shifts, and thus larger offsets in the X-ray spectra. In just the past few years since the launch of NASA’s NuSTAR X-ray telescope, we have been able to use these spectra to measure spins of multiple black holes with unprecedented accuracy. NuSTAR’s ability to see X-rays covering a much wider range of energies compared with previous missions also allows us to rule out other alternative models — like X-ray absorption by interstellar gas clouds — that had been proposed to explain the shape of the spectrum.

The black hole is supposed to be located in Abell 2261, an enormous galaxy cluster that is about 2.7 billion light-years away from our planet. One light-year is the distance that a beam of light travels in one Earth year, which is 9 trillion km. On the scale of the Universe, astronomers measure the distance from stars and galaxies in the time it takes for light to reach us. So, when we look at a celestial object, we are looking at how it appeared that long ago in the past. At 2.7 billion light-years away, the Abell galaxy is at an large distance away from us.

Disappearance of Black Hole

Astronomers are still puzzling over why they aren’t detecting a supermassive black hole (SMBH) in the center of the bright cluster galaxy Abell 2261 (A2261-BCG). Despite recent observations with NASA’s Chandra X-ray Telescope and NASA’s Hubble Space Telescope, there’s little evidence for an expected colossal black hole in a galaxy in the cluster’s core. 

  For years, scientists have observed a large galaxy that lies 2.7 billion light years away from Earth. From every data point they have gathered, there is clear evidence to suggest there is a massive black hole lurking at the center of the galaxy, much like in our own Milky Way. But while scientists are adamant the black hole is there, they haven't been able to find it. Not a trace.

Nearly every large galaxy in the universe contains a supermassive black hole at its centre, with a mass that is millions or billions of times that of the Sun. Astronomers expected this galaxy, at the center of a cluster known as Abell 2261, to contain a supermassive black hole. But data obtained in 1999 and 2004 did not yield signs of such a presence. Fresh observations too have failed to locate any such black hole.

Speaking to online Technology magazine Motherboard, Dr. Gultekin said: "I was very sceptical and thought we would see something at the very center. But that turned out not to be the case. It turned out to not be in any of these locations"

He added that his believe there is a chance that there is a "very stealthy black hole" in the galaxy, one that is dim compared to other supermassive black holes and therefore incredibly difficult to detect. However the possibility that the black hole is missing is even more “exciting” as it would have been ejected by the recoil caused when two supermassive black holes merged during a galactic collision. Supermassive black holes have never been observed merging and finding evidence supporting this hypothetical scenario would be an enormous breakthrough for astronomy, revealing details about the nature of the universe that couldn't be observed in any other way.

As a result of the black hole’s disappearance, scientists are starting to theorize what might happen. The black hole may have been forced out of the galaxy while merging with another galaxy. This is known as a “ bouncing black hole, ” and it would have left a giant galaxy in its wake. There are also theories that the black hole merged with another entity.

Scientists think it is possible that with the merging of two galaxies, two supermassive black holes could have absorbed each other and create a supermassive black hole that is now the core of a larger galaxy. This process has been seen between much smaller black holes before.

From where did it all started

THE MYSTERY BEGAN IN 1999 - Using NASA's Chandra X-ray Observatory, astronomers gathered observations on a galaxy cluster dubbed Abell 2261. At the center of the cluster is a galaxy which outshines the rest: Abell 2261-BCG. This galaxy is some ten times larger than our own Milky Way.

It is well-established that galaxies the same size as the Milky Way or larger contain a massive black hole at their center. The supermassive black hole at the center of the Milky Way is 3.6 million times the mass of the Sun.

But the observations of Abell 2261-BCG did not reveal a black hole at the large galaxy's center.

Astronomers conducted follow up observations in 2004 using NASA's Chandra, and later collected images of the galaxy with NASA's Hubble Space Telescope and the Subaru Telescope, as well as radio emissions measurements using the National Science Foundation's Karl G. Jansky Very Large Array telescope.

And yet: Still no black hole to be found.

Astronomers were undeterred. In 2018, scientists tried Chandra once again, taking further X-ray observations of the galaxy. By imaging the entire galaxy cluster surrounding Abell 2261-BCG, they were able to do a deeper search for the black hole than ever before.

Technically all black holes are hard to find since they're dark — light cannot escape from their depths.

Astronomers usually locate black holes from the motion of the stars next to them, or when they spy certain bright sparks from the black holes which result from the material they draw in towards them, forming a band of dust, gas, and other objects known as their accretion disk.

What could be the possible reason for Disappearance?

A  theory was presented by West Virginia University Team Leader Sarah Burke Spolor in A. a sheet To be published in the American Astronomical Society. Burke Spolor believes there are two possible options; Either there is simply no black hole that scientists previously expected, or the black hole does exist but does not produce enough X-ray radiation to appear in Chandra’s observations.

While the final theory is not as exciting as the merging of black holes and galaxies, it is still a plausible result of a strange discovery. It remains to be seen if we will find out what happened to the supermassive black hole.

Kayhan Gultekin a professor at the University of Michigan's department of astronomy, is the lead author on a new study detailing these scenarios. He tells Inverse he is absolutely sure the black hole is there and he is determined to find it. 

"It’s there, it’s just being very hard to find," Gultekin says.

In the new study, Gultekin and his colleagues have narrowed this mystery down to two strong possible explanations:

THE FIRST SCENARIO suggests the black hole at the center of the galaxy is not gobbling down on much material from its surroundings, and therefore not accreting as much matter.

"So we can't see the telltale signs of the secretion of the matter," Gultekin says. "If it were really bright it would be easy."

THE SECOND SCENARIO is rather out there, literally.

The researchers suggest the black hole may have been expelled from the galaxy after its host merged with another galaxy. The two black holes of the respective galaxies would have merged together, creating a binary black hole.

As two black holes merge, they release a powerful ripple through space and time known as a gravitational wave. The momentum created by the gravitational waves would be strong enough to kick the original black hole out of the galaxy entirely.

This process is known as a recoiling black hole. Astronomers have theorized about these black holes before, but have never observed one.

If it got kicked out Abell 2261-BCG, then the missing black hole is possibly floating aimlessly through space, perhaps surrounded by a few stars.

If this is the case, then the missing black hole is essentially impossible to find. It will remain a mystery to us forever.

Theories related to Black Holes:

1. Matter may travel to the future in a black hole

Black holes run into the problem of infinity, a black hole's mass is crushed to an infinitely dense point that's infinitely small in size. Physically, this doesn't make any sense, so researchers have searched for alternative frameworks to get a handle on black holes. One proposal is known as quantum loop gravity, which suggests that the fabric of space-time is curved very strongly near the center of the black hole. This would result in part of the hole extending into the future, meaning that matter getting sucked into it would time travel forward. So far, this mind-expanding idea remains theoretical.

2. Black holes could be dark matter

Shortly after the Big Bang, the universe should have produced a multitude of tiny black holes. Because these features would be massive objects that give off no light, some physicists have conjectured that these primordial black holes could account for dark matter, that mysterious material that the vast majority of matter in the cosmos is made of. But the idea is controversial, given that data from the Laser Interferometer Gravitational-Wave Observatory (LIGO) has ruled out a universe filled with many minuscule black holes. Perhaps medium-size black holes might still be lurking out there, though observations suggest they would only make up, at most, 1% to 10% of dark matter.

3. Black holes can evaporate

Quantum mechanics provides another way for particles to escape a black hole. According to theory, pairs of subatomic particles are constantly blinking in and out of existence around a black hole's event horizon. Every so often, the configuration is aligned in just the right way to cause one of the partners to fall into the black hole. The particle's identical associate is then propelled away at extremely high speed, robbing the black hole of a tiny bit of energy. This produces what's known as Hawking radiation, after Stephen Hawking, who discovered the phenomenon. Because energy equals mass, this process actually can cause a black hole to shrink and eventually evaporate away over long periods of time.

Stephen Hawking's final theory :

4. Black hole might scramble information

It's hard to square black holes' crushing mass with the laws of quantum mechanics, which hold that information about particles can never be destroyed. But material that slips beyond a black hole's edge should become forever lost to the universe. This condundrum is known as the black hole information paradox; a resolution has eluded scientists to date. Recent research suggests that information that gets scrambled within a black hole could be passed to the outgoing particle partners in Hawking radiation; however, no definitive answer to this paradox has been found.

If you are really interested in this stuff then I will suggest you to watch  Christopher Nolan's movie Interstellar. Interstellar was one of the most mentally-stimulating blockbusters of the 2010s.

The film received four Academy Award nominations for Best Original Score, Best Production Design, Best Sound Mixing, and Best Sound Editing – and the VFX (Visual Effects) were so well regarded that they won the Oscar for Best Visual Effects. Although Interstellar received good-not-great reviews upon release, it’s since garnered more acclaim and it frequently places on lists of the best sci-fi movies ever made.