The mysterious substance that makes up 26 p.c of the mass within the universe performed a key position in early galaxy formation.
On this map of a celestial hemisphere — compiled from knowledge from the eROSITA telescope — the colours mirror the wavelengths of X-rays. Sizzling fuel haloes surrounding galaxy clusters have broad-band emissions (white), as do black holes (white dots); diffuse emissions have lengthy wavelengths (pink); and within the central areas of the Milky Way, dust blocks longer-wavelength emissions, in order that solely short-wavelength X-rays are seen (blue or black). Multicoloured clouds are supernova remnants. Credit score: MPE, J. Sanders for the eROSITA consortium
Cosmologists have lengthy been on the hunt for dark matter, which makes up 80 p.c of the mass within the universe, and but remains to be mysterious. As its title suggests, dark matter doesn’t emit mild, take up mild, or work together with regular matter in any respect. We will solely detect the presence of dark matter via its gravitational results on regular, baryonic matter. For instance, stars and fuel clouds orbit the facilities of galaxies far too rapidly to be accounted for by solely the seen matter, and galaxies transfer round inside clusters far too rapidly. Unseen matter should be serving to these orbits, an impact first observed within the Thirties.
Certainly, the biggest buildings within the universe can solely have developed to their current state aided by the presence of dark matter. In the event that they have been made from solely regular, seen matter, then these buildings, just like the clusters of galaxies which might be residence to a thousand galaxies or extra, merely wouldn’t have had sufficient time to succeed in their current sizes.
So by learning these giant buildings, astronomers can hope to discover a clue as to how dark matter behaves. From there, they will check varied concepts in regards to the nature of dark matter and examine these concepts with observations from the cosmos.
However as a result of clusters of galaxies are so giant, they’re comparatively uncommon. For instance, the nearest galaxy cluster to us is the Virgo cluster, the core of which is 54 million light-years away. If we wish to actually research how dark matter can affect the delivery and evolution of galaxy clusters, we’d like a survey that may seize plenty of them.
Fortunately, galaxy clusters comprise extra than simply galaxies and dark matter. Filling the quantity of every cluster is a sizzling, skinny fuel. This fuel has such a low density that it will register as a vacuum in earthbound laboratories, however is so sizzling that it emits X-ray radiation. This makes galaxy clusters glow brightly at these wavelengths as one of many brightest sources of X-rays on the sky.
In 2019 German and Russian analysis teams collaborated to launch a brand new X-ray satellite, the Spektr-RG mission. Onboard this mission was eROSITA, an X-ray telescope designed to scan all the sky and supply detailed, high-resolution knowledge. Because of the breakdown of relations between Germany and Russia following the latter nation’s invasion of Ukraine, the instrument stopped accumulating knowledge in 2022.
Lately the European House Company introduced the discharge of its first batch of all-sky outcomes, constituting knowledge captured earlier than 2022. The information are publicly out there, and have already been used to strengthen our understanding of dark matter.
All instructed, the eROSITA instrument mapped 5,259 galaxy clusters throughout roughly one-third of all the sky. The variety of clusters within the universe and the distribution of their sizes is carefully linked to the quantity of dark matter. Extra dark matter within the early cosmos will trigger galaxy clusters to type earlier and change into bigger, whereas much less dark matter will produce smaller clusters. The outcomes from the all-sky survey affirm that dark matter performs a important position in shaping these gigantic buildings.
Moreover, the brand new all-sky picture offered sufficient detailed details about galaxy clusters to have the ability to use them as a exact measurement of the total quantity of matter within the universe: 29 p.c of all the mass-energy of the cosmos comes within the type of matter (dark matter making up most of that), with the rest within the type of darkish power. These outcomes agree properly with the established ratios from cosmological satellites like Planck.
The brand new all-sky survey isn’t nearly galaxy clusters. It additionally gives a wealth of details about many high-energy occasions within the cosmos, like pulsars, neutron stars, black holes, and supernovae. The crew will comply with up with extra knowledge captured from the remainder of the sky.
