German Astrophysicist Reinhard Genzel Receives The Nobel Prize

German astrophysicist Reinhard Genzel Receives The Nobel Prize In Physics:

The Max Planck Director is honoured for his observations of the black hole in the galactic centre.

Reinhard Genzel, Director at the Max Planck Institute for Extraterrestrial Physics in Garching, will receive the Nobel Prize for Physics 2020 together with Roger Penrose and Andrea Ghez.

The Nobel Committee honours the scientists for the detection of the black hole in the centre of the Milky Way.

Using high-precision methods, the researchers also observed bursts of brightness in gas from the immediate vicinity of the black hole and a gravitational redshift in the light of a passing star caused by this mass monster.

Reinhard Genzel and his group have achieved several groundbreaking results in galactic and extragalactic astrophysics in recent years.

In 2001, for example, the researchers examined the heart of our Milky Way, which is around 26,000 light-years away, in infrared light. Genzel and his colleagues mapped the movement of stars in the central cluster with high spatial resolution.

With the help of adaptive optics to compensate for air turbulence and a process called speckle interferometry, they were able to precisely measure star speeds in the gravitational field of the supposed black hole up to a distance of 0.1 arc seconds.

From this, Genzel and the astronomers from the Max Planck Institute for Extraterrestrial Physics determined the mass of the black hole with a very high degree of accuracy at around 4.31 million solar masses.

Further studies by Reinhard Genzel's group showed that both the mass spectrum and the geometry of the stars in the centre of the galaxy are unusual.

The scientists also discovered bursts of radiation in the infrared range, which likely originate from gas near the inner accretion disk of the black hole.

Only last year did Reinhard Genzel succeed in demonstrating the so-called gravitational redshift on a star for the first time.

Astronomers use sensitive instruments such as Gravity, Sinfonia and Naco to observe the galactic centre.

They all belong to the Very Large Telescope of the European Southern Observatory (ESO), were built under the direction of the Max Planck Institute for Extraterrestrial Physics and pattern the sky in infrared light.

The researchers turned their attention to a star named S2 and tracked it on its orbit around the black hole, which it came particularly close to in 2018.

The closest distance between S2 and the black hole on May 19 was about 14 billion kilometres.

The star moved at a speed of more than 25 million kilometres per hour - corresponding to almost three per cent of the speed of light. It takes about 15 years to complete one cycle.

The scientists compared the position and velocity measurements from Gravity and Sinfonias well as those from earlier observations of S2 with the predictions of Newtonian gravitational physics, general relativity and other theories of gravity.

In fact, the new results contradict Newton's predictions but agree perfectly with those of general relativity.

The measurements clearly showed an effect that is known as gravitational redshift: the light from star S2 is stretched to longer wavelengths by the very strong gravitational field of the black hole and therefore appears reddish.

And this change in wavelength agreed exactly with the prediction of Einstein's general theory of relativity.

This was the first time that the researchers observed this deviation from the predictions of the simpler Newtonian theory of gravity in the motion of a star around a supermassive black hole.

Also in 2018, Reinhard Genzel published a work on the observation of brightness outbursts near the galactic black hole. The researchers saw three such flares. They all had the same orbital radii and the same orbital periods.

The movement of these three hot spots in the galactic centre can be explained by a simple orbit model, the radius of which is three to five times larger than that of the event horizon of the black hole.

Genzel's group found out that gas swirls around it at a speed of 30 per cent the speed of light - in line with theory.

It was not until the spring of this year that a team led by the Max Planck Director made another significant discovery: Years of observation of the orbit of the star S2 showed that it does not remain stationary in space, but rather that it progresses slowly.

That means several revolutions of S2 result in the shape of a rosette. Albert Einstein had also prophesied this effect in his general theory of relativity, and he explains, for example, the long-known rotation of Mercury's orbit.

This discovery was also successful with the Gravity instrument, which combines the light from all four eight-meter mirrors of ESO's Very Large Telescope.

Thanks to this technique called interferometry, Gravity generates the power of a virtual telescope with an effective diameter of 130 meters.


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