Massive neighbourhood
What would Albert Einstein say about this space discovery? He theorised it, but did not fully believe it himself during his lifetime: the existence of black holes.
It was to take a few more decades but, in the 1970s, Cygnus X-1 was the first real detection of a black hole in our Milky Way galaxy. Since then, many “Black Holes” have been documented. However, researchers from the Observatoire de Paris discovered a very special one in spring 2024: the most massive stellar black hole ever found in the Milky Way. The sensation: “Gaia Black Hole 3 (BH3)” is only about 2000 light years away from our earth. The new discovery in our neighbourhood shook up astrophysics.
Black holes: star graves or space hoovers?
Black holes are created, for example, when massive stars reach the end of their life cycle. Simply put, in their stable phase of life in the star, the centrifugal force (from the “burning energy”) and the gravitational force (caused by the mass) balance each other out. As a star ages, however, the “burning energy” decreases more and more and is finally no longer sufficient to balance the gravity. At some point, this is stronger than the centrifugal force and causes the star to collapse. Due to the large mass, this gravitational force is sufficient to practically concentrate the star at one point during the implosion.
The resulting black holes live up to their name; they are extremely massive objects in space that devour everything that comes too close to them – even light. When planets, stars or beams of light pass their so-called event horizon, they disappear forever into the most massive point of the black hole: the singularity.
Research divides dark, attractive space objects into different categories based on their mass dimensions: among others, stellar black holes (with around 10 solar masses), medium-gravity black holes (around 1000 solar masses) and supermassive black holes (approx. 10,000,000,000 solar masses, i.e. 10 billion). A comparison:
Gaia BH3 is a stellar black hole with 33 solar masses. The largest black hole discovered to date in our Milky Way is the supermassive black hole Sagittarius A* with around 4 million solar masses. Sagittarius A* is therefore much larger than Gaia BH3, but fortunately much further away from Earth at just under 27,000 light years.
The discovery of Gaia BH3 – a foreseeable accident
Since black holes do not emit light on their own, they are difficult to detect. One of the things it reveals is the gravitational effects it causes in its surroundings.
A research team led by Pasquale Panuzzo and Elisabetta Caffau tracked down Gaia BH3 using the European Space Agency’s (ESA) Gaia space telescope. With the help of this telescope, they had been observing an old giant star in the constellation of Eagle for several years. This star exhibited fluctuations in its orbit over a longer period of time – it was, so to speak, making a U-turn. This was seen as an indication that it was being orbited by an invisible and extremely massive object.
Detailed analyses and calculations confirmed the assumption: the star is indeed orbiting a dormant black hole with a mass around 33 times that of the sun.
From theory to proof: black holes as an extreme example of curved spacetime
Since the time of Albert Einstein, many important scientists have contributed to the current state of research on black holes. But everything is based on his ingenious idea: without Einstein’s theory of relativity and his pioneering ideas on the nature of gravity, modern astrophysics would be inconceivable and inexplicable.
While Isaac Newton still described gravity as an invisible force between masses, Einstein theorised that it represents a curvature of spacetime. As a compelling derivation of this, he extended the hitherto three-dimensional space by the factor of time.
With his general theory of relativity, he predicted something that he himself was never able to prove during his lifetime: there must be objects in space that, due to their high mass, bend spacetime so strongly that above a certain limit nothing – not even light – can escape their gravity. Black holes are precisely these objects.
Gaia BH3 discovery: we know that we don’t know everything yet
The discovery of Gaia BH3 caused a lasting stir in scientific circles. Until now, stellar black holes of this size have only been detected in distant galaxies.
The discovery called into question current theories of stellar evolution. What sounds like a step backwards is actually a big step forward in astrophysics: every black hole discovered, especially such a significant one, helps us to understand the universe and its origins even better.
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Sources:
https://www.ardalpha.de/wissen/weltall/astronomie/schwarzes-loch-weltall-102.html
https://www.mpg.de/schwarze-loecher
https://www.deutschlandfunk.de/einstein-auf-dem-pruefstand-11-die-existenz-von-schwarzen-100.html
https://www.aip.de/de/news/gaia-bh3/
https://www.swr.de/wissen/massereiches-schwarzes-loch-in-der-milchstrasse-entdeckt-100.html
https://www.astronomische-gesellschaft.de/de/Nachrichten/schwarzes-loch-milchstrasse
