NASA scientists have encountered a mass of black holes lurking in the center of our Milky Way galaxy. The remarkable discovery was made using the data returned from NASA's Chandra X-ray Observatory.
The newly discovered black-bound premium consists of stellar black holes, which typically weigh between five and five times the mass of the sun. These newly identified black holes were found within three light years – a relatively short distance on cosmic scales – of the supermassive black hole at the center of our galaxy, known as Sagittarius A * (Sgr A *).
Theoretical studies on the dynamics of stars in galaxies have suggested that a large population of stellar masses could drive black holes – as many as 20,000 – inwards over the eons and accumulate around Sgr A *. This recent analysis using Chandra data is the first observation of such a black hole premium.
A black hole in itself is invisible. A black hole – or a neutron star – trapped in a close orbit with a star will draw gas from its companion (astronomers call these systems "x-ray binaries"). This material falls into a disk and heats up to millions of degrees, producing x-rays before disappearing into the black hole. Some of these X-ray binaries appear as point sources in the Chandra image.
A research team led by Chuck Hailey of Columbia University in New York searched for black-hole X-ray binaries with Chandra data near Sgr A *. They examined the X-ray spectra – that is, the amount of X-rays observed at different energies – from sources within about 12 light-years of Sgr A *.
The team then selected sources with similar X-ray spectra from known X-ray binaries, which have relatively large amounts of low energy X-rays. Using this method, they discovered 14 X-ray binaries within approximately three light-years of Sgr A *. Two X-ray sources, which probably contained neutron stars based on the discovery of characteristic bursts in previous studies, were then removed from the analysis.
The dozen remaining x-ray binaries are identified in the marked version of the image using red circles. Other sources of relatively high levels of high energy X-rays are marked in yellow and consist mainly of binaries with white dwarf stars.
Hailey and his associates concluded that much of these dozen X-ray double stars are likely to contain black holes. The variability they have shown over time scales of years differs from that expected for X-ray diffraction binaries with neutron stars.
Only the brightest X-ray binaries with black holes are likely to be detectable at the distance from Sgr A *. , Therefore, the data in this study suggest that a much larger population of weaker, unrecognized X-ray binary – at least 300 and up to a thousand – should be present with stellar black holes around Sgr A *.
This population of black holes with companion stars near Sgr A * might give some insight into the formation of X-ray binaries from close encounters between stars and black holes. This discovery could also influence future gravitational wave research. Knowing the number of black holes in the middle of a typical galaxy makes it easier to predict how many gravitational wave events can be associated with them.
An even larger population of stellar black holes without companion stars should be present near Sgr A *. According to the theoretical reworking of Aleksey Generozov from Colombia and his colleagues, more than 10,000 black holes and up to 40,000 black holes should exist in the center of the galaxy.
While The Authors Strongly Advocate the Black Hole Explanation It can not be ruled out that up to about half of the observed dozen sources consist of a population of millisecond pulsars, that is, very fast rotating neutron stars with strong magnetic fields.
On April 5, a paper with these results th issue of the journal Nature appeared. NASA's Marshall Space Flight Center in Huntsville, Ala., Heads the Chandra program for NASA's Scientific Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts controls Chandra's science and flight operations.