Scientists have uncovered the origin of three mysterious signals coming from the centre of the Milky Way.
For years, astronomers have struggled to understand the strange spikes of energy that blare out from the heart of our galaxy.
But researchers now say a very specific type of dark matter, known as ‘excited dark matter’, is responsible.
Dark matter is an elusive substance which makes up roughly a quarter of the universe, but cannot be observed through any normal means.
Since dark matter doesn’t interact with normal matter, even our most powerful telescopes cannot see it directly.
However, scientists believe that this strange substance may be indirectly producing the baffling behaviour of our galaxy’s turbulent core.
Lead author Dr Shyam Balaji, of King’s College London, says: ‘When we look at well–known astrophysical events, like star explosions, they haven’t been able to provide a full explanation for mysteries like the specific energy and shape we’ve observed coming from the centre of the Milky Way.
‘Now, we’ve shown how one excited dark matter model could account for at least two – possibly even three – of these kind of unexplained signals at once.’
Scientists have discovered the origin of three mysterious signals coming from the centre of the universe, showing that a mysterious substance called excited dark matter could be the explanation. Pictured: Predictions from the dark matter model (pink) compared to telescope observations (red crosses)
The heart of the Milky Way is an exceptionally chaotic and violent place, where immense forces pull and crush clouds of dense gases into fast–moving stars.
At the very core is the supermassive black hole Sagittarius A*, which has a mass around four million times greater than that of the sun.
The intense gravity and heat release radiation that can be seen by telescopes out in space, but scientists haven’t been able to explain everything they’ve observed.
For example, scientists have found a sharp spike in gamma–ray radiation at an extremely specific wavelength – known as the 511–keV emission line.
This isn’t something that fits with our established picture of how normal matter functions, so scientists have had to look elsewhere for an explanation.
In a new paper, published in The Astrophysical Journal Letters, scientists showed that these signals could have been caused by ‘excited dark matter’.
Dr Balaji told the Daily Mail: ‘Excited dark matter is a scenario where dark matter particles can briefly jump into a slightly higher–energy state when they collide with each other.
‘When they fall back to their normal state, they release that extra energy by producing an electron and its antimatter partner, a positron.’
Scientists say that the galactic core might be filled with a substance called excited dark matter. This cannot be seen directly, but may be responsible for the strange energy signals seen by telescopes
These positrons generate signals that can be picked up by deep–space telescopes such as the European Space Agency’s INTEGRAL mission, located outside the Earth’s radiation belts at an altitude of 37,000 miles (60,000 km).
The researchers looked at data from INTEGRAL and compared it to a model of how positrons might move through space.
This showed that collisions between the positrons produced by excited dark matter could lead to a spike in gamma–ray radiation that matches the mysterious 511–keV emission line.
But the scientists didn’t stop there, as they soon found that their excited dark matter model could explain even more strange signals.
In particular, they found that the release of positrons could be the origin of a very high–energy light coming from the centre of the galaxy, known as the 2 MeV gamma–ray continuum.
Dr Balaji says: ‘The signal requires positrons with very specific energies of only a few million electron volts. Most conventional astrophysical sources, such as supernovae or cosmic rays, tend to produce particles that are either much more energetic or distributed across the galaxy in the wrong way.
‘The excited dark matter scenario naturally produces positrons in exactly this energy range.’
In addition, they suggest their model could potentially explain an unusually high level of ionisation in a clump of gas within a region called the Central Molecular Zone (CMZ).
Scientists also believe that excited dark matter could explain the strange ionisation of gases in a region near the galactic centre called the Central Molecular Zone (pictured)
This crowded region, located 28,000 light–years from Earth, is a vast reservoir of swirling matter and stars that contains almost 80 per cent of the galaxy’s dense gas.
However, sources such as cosmic rays – high–energy particles ejected by complex processes in the inner galaxy – haven’t explained why this gas appears to be so heavily ionised.
The researchers now suggest that the answer could well be the strange behaviour of excited dark matter.
Co–author Damon Cleaver, a PhD student at King’s College London, says: ‘If one mechanism could account for several long–standing unexplained observations in space, it gives a much clearer direction for future research.
‘Within the next generation of space missions, we may finally be able to test the theory of whether dark matter is behind some of the Milky Way’s most persistent mysteries and learn more about the mysterious substance itself in the process.’
Dark matter: The mysterious substance that makes up 27% of the universe that scientists cannot confirm
Dark matter is a hypothetical substance said to make up roughly 85 per cent of the universe.
The enigmatic material is invisible because it does not reflect light, and has never been directly observed by scientists.
Astronomers know it to be out there because of its gravitational effects on known matter.
The European Space Agency says: ‘Shine a torch in a completely dark room, and you will see only what the torch illuminates.
Dark matter is a hypothetical substance said to make up roughly 27 per cent of the universe. It is thought to be the gravitational ‘glue’ that holds the galaxies together (artist’s impression)
‘That does not mean that the room around you does not exist.
‘Similarly we know dark matter exists but have never observed it directly.’
The material is thought to be the gravitational ‘glue’ that holds the galaxies together.
Calculations show that many galaxies would be torn apart instead of rotating if they weren’t held together by a large amount of dark matter.
Just five per cent the observable universe consists of known matter such as atoms and subatomic particles.
