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By combining a new image of a giant galaxy cluster with older X-ray data, scientists at the European Space Agency (ESA) how the cluster’s galaxies are surrounded by huge amounts of gas that can reach scorching temperatures of up to 100 million degrees Celsius (180 million degrees Fahrenheit).
It was the galaxy cluster, Abell 2390 recently imaged at ESAs Euclid’s missiondesigned to study dark dark and dark energy asking gravitational lensing occurrences in galaxy clusters. Because there is so much mass in these clusters – up to ten trillion solar masses even – they are able to bend the skeleton of it space–time around them, enveloping it so much that light from distant galaxies in the background becomes greatly magnified. It’s like you’re looking at them through a giant magnifying lens. If we zoom in on the core of Abell 2390, we see the lensing effect at its most dramatic, stretching, stretching and amplifying the light of other galaxies billions of light-years away.
However, most of the mass of galaxy clusters is not found in galaxies. In fact, they barely contribute to 5% of the total mass of the cluster. The major contributors are the hot interstellar gas in the cluster, which accounts for about 15% of the cluster’s mass, and invisible dark matter, which accounts for a whopping 80% of Abell 2390’s mass.
Although we can infer the presence of dark matter from the amount of gravitational lensing, we cannot see it. We can see the interstellar gas, however, thanks to the X-ray vision of ESAs XMM- Newton mission, which detected this gas in Abell 2390 all the way back in 2001.
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In this new composite view, we see the Euclid image of Abell 2390, located 2.7 billion light-years away in the constellation of Pegasus, the Winged Horse. Euclid’s image is incredible; it is a wide-field image, the field of view through its 1.2 meter (3.9 ft) aperture telescope spanning 1.25 by 0.73 square degrees. The image contains about 50,000 galaxies, many of which are not in Abell 2390, which can be seen in the center of the image and which itself contains thousands of galaxies. The most distant background galaxies, far beyond even Abell 2390, appear red because their light redshifted because of the expansion of the universe. A handful of foreground stars they can also be seen, with their six-lobed diffraction spikes singled out.
On the other side of Euclid’s visible-light spectrum is the XMM-Newton detector of X-ray emission from the cluster. This is produced by ionizing hydrogen gas with a temperature between 10 million and 100 million degrees Celsius (18 million to 180 million degrees F). At such a temperature, the gas only radiates in X-rays, so what we see here as the blue glow is a false color representation of the X-ray signal. The X-rays are brightest towards the center of the cluster, where the inner gas is hottest and most concentrated.
At the heart of Abell 2390, amidst this extremely hot gas, is the brightest cluster galaxy, or BCG, known. Every major galaxy cluster has one of these — in the nearby Virgo Cluster, the BCG is Messier 87. In other words, the BCG is a giant elliptical galaxy with active supermassive black hole at its core, feedback from which — in the form of radiation outflows — can heat the interstellar gas and even prevent star formation in the other galaxies of the cluster.
I results published earlier this yearBCG Abell 2390 views with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile revealed a huge plume containing over 10 billion solar masses worth of molecular gas stretching nearly 50,000 light year away from the BCG. Scientists believe that the dust from another galaxy passing by, or even merging with, the BCG in the crowded halo of Abell 2390 is likely to have been a gravitational disturbance. The disturbance could such an event would result in sufficient decoupling, or separation, from the gas within the cluster by BCG and the surrounding dark matter, leaving behind a trail of molecular gas similar to that found by ALMA in the flour.
Meanwhile, at radio wavelengths, the Low Frequency Array (LOFAR) in Europe detected several lobes of radio-emitting particles around BCG Abell 2390s. These lobes are formed by an intermittent but powerful jet that originates from the active black hole in the middle of the BCG. The lobes are of different ages, and are pointing in different directions, suggesting that the jet – and thus the orientation of the black hole and the surrounding accretion disk of gas that feeds the jet – is going before it. In other words, it is howling in a regular fashion, the jet tracing out a circle above the black hole’s rotating axis.
The jets can heat the medium within the surrounding cluster, but at present they appear to be in a quiescent phase and the hot X-ray emission gas is slowly cooling and falling back onto the BCG and other galaxies in the cluster, where the gas could cool. there could be a new form stars.
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One new innovation from Euclid is the ability to detect billions of stars being ripped from their galaxies by tidal gravitational forces at work in the cluster’s turbulent environment. Individually the stars are far too faint to be seen at such great distances, but together, they add an eerie glow, which is enhanced in the Euclid image. By following when these rogue interstellar stars meet, drawn in by gravityastronomers can look for the dark matter in Abell 2390.
Euclid’s first images of the universe, including one of Abell 2390, were released in May. The spacecraft, which was launched back in July 2023, has now begun a six-year mission to map the dark universe by observing the billions of galaxies and galaxy clusters spread over 10 billion years of cosmic history.
