galaxies

Astronomers Find the Most Massive Supercluster to Date

The Earth’s place in space is a fairly familiar one with it orbiting an average star. The star – our Sun – orbits the centre of our Galaxy the Milky Way. From here onwards, the story is less well known. The Milky Way is part of a large structure called the Laniakea Supercluster which is 250 million light years across! That really is a whacking great area of space and it contains at least 100,000 galaxies. There are larger superclusters though like the newly discovered Einasto Supercluster which measures an incredible 360 million light years across and is home to 26 quadrillion stars!

When I give public lectures, I always get a strange satisfaction out of telling the audience that galaxies don’t exist! I go on to explain that, like a city which is a collection of stuff, galaxies are collections of things bound together under the force of gravity. A typical galaxy is simply a collection of stars, nebulae, clusters, planets, comets and so on, take them away and a galaxy won’t exist! Superclusters are largely the same, just a collection of galaxies bound together (well, not completely) under the force of gravity. 

Hot stars burn brightly in this image from NASA’s Galaxy Evolution Explorer, showing the ultraviolet side of a familiar face. At approximately 2.5 million light-years away, the Andromeda galaxy, or M31, is our Milky Way’s largest galactic neighbor. The entire galaxy spans 260,000 light-years across — a distance so large, it took 11 different image segments stitched together to produce this view of the galaxy next door. The bands of blue-white making up the galaxy’s striking rings are neighborhoods that harbor hot, young, massive stars. Dark blue-grey lanes of cooler dust show up starkly against these bright rings, tracing the regions where star formation is currently taking place in dense cloudy cocoons. Eventually, these dusty lanes will be blown away by strong stellar winds, as the forming stars ignite nuclear fusion in their cores. Meanwhile, the central orange-white ball reveals a congregation of cooler, old stars that formed long ago. When observed in visible light, Andromeda’s rings look more like spiral arms. The ultraviolet view shows that these arms more closely resemble the ring-like structure previously observed in infrared wavelengths with NASA’s Spitzer Space Telescope. Astronomers using Spitzer interpreted these rings as evidence that the galaxy was involved in a direct collision with its neighbor, M32, more than 200 million years ago. Andromeda is so bright and close to us that it is one of only ten galaxies that can be spotted from Earth with the naked eye. This view is two-color composite, where blue represents far-ultraviolet light, and orange is near-ultraviolet light.

Superclusters like Laniakea and Einasto (which is 3 billion light years away) are among the largest structures in the Universe. The discovery of this latest supercluster has been named after Professor Jaan Einasto who was a pioneer in the field of superclusters and celebrated his 95th birthday on 23 February 2024. 

When it comes to visualising the sheer size of these structures imagine an average coin (I really don’t think it matters too much which coin you imagine) on a football pitch. This coin represents the Milky Way Galaxy and the length of the pitch would be the extremities of the supercluster! You might also imagine the Sun as a golf ball and the entire collective mass of the supercluster as Mount Everest in comparison!

A study by MIT physicists suggest the Milky Way’s gravitational core may be lighter in mass, and contain less dark matter, than previously thought. Credits:Credit: ESA/Gaia/DPAC, Edited by MIT News

The announcement came from a group of international astronomers from the Tartu Observatory who also surveyed 662 other superclusters. Their work (which was published in the Astrophysical Journal) also revealed some interesting dynamics inside superclusters for example, they found that the galaxies within a supercluster are receding from each other slower than the general expansion of the universe. This is due to the gravitational pull of the supercluster acting as a brake on the expansion. Whilst it is slowing the expansion of the area it is not slowing it enough to stop the galaxies from drifting apart given enough time. Superclusters should be considered temporary, changing phenomena.

They also found that there was a relationship between the density and size of a supercluster. The relationship was an inverse square relationship meaning that the density of a supercluster decreases with the square of its size. 

Source : Einasto Supercluster: the new heavyweight contender in the universe

Mark Thompson

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