Our sun becomes a black hole

19.02.2021 10:35

Black hole in the Milky Way more massive than assumed

Blandina Mangelkramer Press and communication
Friedrich-Alexander University Erlangen-Nuremberg

FAU astrophysicists contribute to the latest findings on Cygnus X-1

An international team of renowned astrophysicists including the Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) has gained new knowledge about Cygnus X-1. The black hole and its companion star in the Milky Way are further away from Earth and much more massive than previously thought. At the same time, the project provides new answers to the question of how black holes arise in the first place. The results have been published in the leading journal "Science". *

The first indication came as early as 1964: Two Geiger counters on board a suborbital rocket that was fired from New Mexico registered a strong X-ray source in our Milky Way. Eight years later, the American astronomer Tom Bolton discovered that this X-ray source orbits the star HDE 226868, a so-called blue giant. Bolton concluded from this that Cygnus X-1 - as the invisible source is called - must be a black hole. This assumption was confirmed by later observations. "Cygnus X-1 is the first black hole that was discovered in our Milky Way", explains Prof. Dr. Jörn Wilms, astrophysicist at the FAU University Observatory.

The actual distance of the system from Earth has so far only been roughly estimated, as has the masses of the black hole and its companion star. Wilms has therefore initiated an ambitious project to which an international team of renowned astronomers has come together. The researchers used the Very Long Baseline Array, a cluster of ten radio telescopes distributed throughout the USA, to carry out a precise parallax measurement. "The measurement is based on the principle that you can determine the distance of an object by looking at it from two different locations," says Jörn Wilms. "In our case, the different observation positions result from the movement of the earth around the sun."

Loss of matter from bright stars less than expected

Over a period of six days, the scientists working with project leader James Miller-Jones from the International Center for Radio Astronomy Research (ICRAR) observed the Cygnus system and recorded over 2000 measured values. The result: Cygnus X-1 is significantly further away from Earth than previously assumed - about 7200 light years instead of the previously estimated 6100 light years. "This calibration also shows that Cygnus has to be significantly larger," explains Jörn Wilms. “We have calculated that the black hole is more than 20 times as massive as the sun,” says Jörn Wilms. "That exceeds previous estimates by 50 percent."

At the same time, this finding sheds new light on the formation of black holes in general: Until now, research has assumed that bright stars lose a great deal of mass to their surroundings before the supernova explosion. Wilms: “With stellar winds, matter is practically blown away from the surface. In order for a black hole to become as massive as Cygnus X-1, this loss of mass must be significantly less than we thought. "

Based on the current measurement data, the researchers assume that the black hole in the Cygnus X-1 system began its life as a star that was around 60 times the size of the sun and collapsed tens of thousands of years ago. Despite its gigantic size, it orbits its companion star HDE 226868 in just five and a half days, with the orbit being only a fifth of the distance between the earth and the sun. Cygnus X-1 rotates incredibly fast - very close to the speed of light and therefore faster than any other black hole found so far. The extremely strong X-ray radiation is caused by the fact that the companion star loses part of its mass to the black hole, forming a disk of gas that heats up to several million degrees through friction.

New radio telescope is set to reveal more secrets

"Black holes are still among the best-kept secrets in the universe," says Jörn Wilms. "With our project we have been able to reveal another part of this secret." In the coming year, construction of the Square Kilometer Array (SKA) is to begin in Australia and South Africa, which will once again exceed the sensitivity of what is currently the largest radio telescope in the world and the universe in even greater detail can map. Astro research hopes that this will provide new impulses for the understanding of exotic and extreme cosmic objects that have so far remained hidden from us.

* https://science.sciencemag.org/content/early/2021/02/17/science.abb3363
"Cygnus X-1 contains a 21-solar mass black hole — Implications for massive star winds"

Media contact:
Prof. Dr. Jörn Wilms
Dr. Karl Remeis Observatory Bamberg - FAU Astronomical Institute
Tel .: 0951 / 95222-13
[email protected]

Scientific contact:

Prof. Dr. Jörn Wilms
Dr. Karl Remeis Observatory Bamberg - FAU Astronomical Institute
Tel .: 0951 / 95222-13
[email protected]

Original publication:


Additional Information:

http: // Animated explanatory video at:
https: //www.fau.de/2021/02/news/wissenschaft/schwarzes-loch-in-der-milchstrasse -...

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Physics / astronomy
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