We imagine that there is an empty, dark, soundless, space, or hole when we hear about black holes, but let not its name fool you.
The black hole is a tremendous amount of matter packed into a tiny area. Its size is likened to a star ten times more massive than the Sun and compressed into a sphere as big as the diameter of New York City.
The ideas, news, and stories of black holes have been around for centuries, and the most famous was Einstein’s theory of general relativity, which states that when a massive star dies, it leaves a small dense remnant core. Yet if the mass of the core exceeds thrice of the Sun’s mass, the gravitational force overwhelms other forces, thus producing a black hole.
Today, we now have references for these strange but fascinating objects in space with the help of NASA’s technology.
In 1974, Martin Rees, a British cosmologist, and astrophysicist, suggested that a supermassive black hole exists within the active galactic nuclei.
The Milky Way, like the other massive galaxies, is stick together by a supermassive black hole at its center. Our galaxy’s supermassive black hole called Sagittarius A* or Sgr A* continuously pulls stars, dust, and other matters. This compact object is approximately one Astronomical Unit or about 93 million miles in size.
Over the years, astronomers gather and record pieces of evidence through the observed motions of gas and stars to prove that something very massive truly lies at the center streamers of the mini-spiral orbiting Sgr A*. They have also suggested that there is an estimated six million solar masses that lie within 10 arcseconds of Sgr A* using the velocities of the gas from the Doppler Effect spectral lines.
However, there was no clear proof of the supermassive black hole. And the amount of matter could be accounted for by a high density of stars.
Since 1995, it was observed that a compact mass of early-type stars encircling the radio position of Sgr A*. They have large proper motions considering their 24 million light-year distance from the Earth.
A group from UCLA and Andrea Ghez used a 10m Keck telescope on Mauna Kea Hawaii, and Reinhard Genzel and Andreas Eckart used the 8-m VLT telescopes in Chile tried to track the stars. They take advantage of the high-resolution and sensitivity telescopes in gathering data using near-infrared images they collected once or twice a year.
Unfortunately, despite the advanced technology astronomers used, such as the large diameters of the Keck and VLT telescopes, several factors significantly affected the data gathering, like air turbulence and the atmosphere’s high temperature.
Later on, astronomers shifted to use Adaptive Optics (AO) systems, which increase the sensitivity of observations. It is capable of correcting data before recording, despite atmospheric turbulence.
Studies reveal that supermassive black holes are not unique to the Milky Way, and astronomers still have various speculations as to how they form.
Using The Event Horizon Telescope, scientists snapped an image of black hole M87 in 2019. (https://www.space.com/first-black-hole-photo-by-event-horizon-telescope.html) It is was found at the center of the galaxy Virgo A which is about 53 million light-years away and as big as the solar system and about 6.5 billion times the mass of the sun.
So far, astronomers have identified three types of black holes: stellar black holes, supermassive black holes, and intermediate black holes.
In the past, physicists believed that singularities such as a black hole, were featureless, and only had three properties: mass, electric charge, and angular momentum. Until 2016, when Stephen Hawking, along with others, published a paper that stated black holes have “soft hairs” or have distinctive features.
The paper, which was published in preprint journal arXiv, proposes that the information devoured by a black hole is stored in these electric hairs. (https://arxiv.org/pdf/1601.00921.pdf) However, it turned out that these “hairs” eventually, lose. So this study also did not fully solve the paradox on black holes.
Have we misunderstood black holes?
If this supermassive black hole is not yet 100 percent proven to have existed, then maybe it did not exist, and we have only misunderstood them. This idea is strongly believed by Kevin Croker, an astrophysicist, and Joel Weiner, a professor emeritus in mathematics, both from the University of Hawaii at Mānoa. They looked at Friedmann’s equations, which are simplified from Einstein’s theory of general relativity.
Also, George Chapline, an American theoretical physicist from Lawrence Berkeley National Laboratory, thinks that the collapse of the massive stars leads to the formation of stars that contain dark energy and not generate black holes, which we believed in for a long time.
- Supermassive black hole (Wikipedia)