Einstein’s Theory of Relativity Reveals Lonely Black Hole

A lone, stellar-mass black hole has been discovered for the first time by a team of scientists involving the critical expertise of researchers at the University of St Andrews.

The black hole’s presence was revealed by a small shift in the position of an observed background star due to the curvature of spacetime by the black hole in accordance with Einstein’s theory of relativity.

This new discovery opens the door to obtaining demographic data for black holes across the galaxy, providing important observational data about the late stages of stellar evolution. The measurements, at the extreme limits of the Hubble Space Telescope’s capabilities, were a team effort by academics at the University of St Andrews and the Space Telescope Science Institute (STScI).

Theoretical models suggest that there may be 100 million black holes hidden among the hundreds of billions of stars in the Milky Way. These have escaped detection because they do not emit light or other forms of their own electromagnetic radiation (the only exception being an undetectable small amount of Hawking radiation), nor do they reflect light from other luminous bodies like planets can.

However, a black hole’s own gravity does affect the path of light in its environment, bending it by an amount proportional to its mass, explained by Albert Einstein’s general theory of relativity due to massive bodies curving space-time.

dr. Martin Dominik, Lecturer in the School of Physics and Astronomy at the University of St Andrews, said: “Einstein did it again: Black holes make themselves invisible, but they can’t hide their gravitational pull. It was amazing to see how two observable signatures of the black hole’s gravitational deflection matched: the shift in position and an apparent brightening of the observed background star.”

Until now, all known black holes within the stellar mass range have been in binary systems, in which two astronomical bodies orbit each other due to gravitational attraction.

The observed deflection of light by gravity is the same effect that caused the change in the position of stars near the sun’s edge, measured by Arthur Eddington and colleagues during the solar eclipse of May 29, 1919, and those observations ultimately made Einstein famous.

However, for such a deflection of light to be substantial, an observed star must be closely aligned in the sky with an intermediate massive body, and such alignments are rare.

With a chance of one in a million, special studies such as OGLE (Optical Gravitational Lensing Experiment) or MOA (Microlensing Observations in Astrophysics) use 1 to 2 m-class telescopes to monitor hundreds of millions of stars toward the bulge of the Earth. the Milky Way to capture ongoing so-called gravitational microlensing events.

These are characterized by a transient brightening of the observed star due to the deflection of the light, changing the amount of total light received in two unresolved images.

One such gravity microlensing event independently detected by either team in 2011, also known as MOA-2011-BLG-191 or OGLE-2011-BLG-0462, had an unusually long duration, which could be due to either be due to the fact that the intermediate body moved slowly in the sky relative to the observed rut star, or alternatively because the mass of the deflector is large. Since stellar-mass black holes are expected in the range of 3 to 20 solar masses, compared to a typical stellar-mass gravity lens of 0.3 solar masses, and since the event was also compatible with the lens object being dark, it made it a good candidate for microlensing through a black hole.

So a team led by Dr. Kailash Sahu, who works at the Space Telescope Science Institute (STScI) in Baltimore and is a longtime associate of Dr. Dominik, the Hubble Space Telescope (HST) for the next six years to track the position of the source star that caused this event. As they had researched 20 years ago, the positional shift of the light’s center of gravity, composed by the two unresolved images, is observable over a much longer period of time than the illumination, and these observations would unequivocally yield the mass of the gravitational lens.

These measurements proved challenging: Not only was the intended target close to a much brighter star, which cannot be resolved on ground images, but the gravitational deflection of light is quite small. Right at the limits of what is possible with HST, the positional measurements have an uncertainty of only 0.2 milli-arcseconds, which is 10,000 times less than the 2-arcsecond bend angle that Eddington looked at, and about the 6 billionth part of the full angle.

The degree of positional shift of the bronze star relates both to the mass of the gravitational lens and to its distance, while the magnitude of the Earth’s orbit forms a ruler for the distance, leading to a shift of the relative positional angle between the bronze star and the intermediate lens, which is prominently visible in the illumination of the source as a function of time. Together, these effects gave a lens mass of about 7 solar masses, as well as a distance of 1.6 kpc (or about 5000 light-years).

Such mass is above the range expected for other single or binary objects of negligible brightness. Stellar-mass black holes are the end product of massive stars that are at least 20 times more massive than the Sun. These stars explode as supernovae and the remaining core is crushed by gravity into a black hole. Because the self-explosions of stars are not perfectly symmetrical, the remaining black hole can take a kick. The inferred transverse velocity of the gravitational lens turned out to be an outlier among stars at a similar distance, further confirming that it is indeed a black hole.

There is considerable scope for further detection of isolated stellar-mass black holes, using the same approach with ESA’s Gaia satellite, aimed at accurately mapping stellar positions and velocities throughout the Milky Way and, unless stellar-mass black holes are much less common than we currently think the capabilities of the Nancy Grace Roman Space Telescope, due to launch within the next five years, will make this a routine job.

dr. Dominik added: “We have identified the gravitational deflection of light by a dark object of seven solar masses in the Milky Way. It is an isolated black hole of stellar mass that could not hide, and many others will fail in the near future as well.”

/public release. This material from the original organisation/author(s) may be of a point in time, edited for clarity, style and length. The views and opinions are those of the author(s). View full here

#Einsteins #Theory #Relativity #Reveals #Lonely #Black #Hole

Leave a Comment

Your email address will not be published.