Einstein rings and dark matter
By Rossana Ruggeri, The University of Queensland
Physicists imagine many of the matter within the universe is made up of an invisible substance that we solely learn about by its oblique results on the celebrities and galaxies we are able to see. We’re not loopy! With out this dark matter, the universe as we see it will make no sense.
The character of dark matter is a longstanding puzzle. Nonetheless, a new study by Alfred Amruth on the College of Hong Kong and colleagues, printed in Nature Astronomy, makes use of the gravitational bending of sunshine – Einstein rings – to carry us a step nearer to understanding.
Invisible however omnipresent
The rationale we expect dark matter exists is that we are able to see the results of its gravity within the conduct of galaxies. Particularly, dark matter appears to make up about 85% of the universe’s mass. And many of the distant galaxies we are able to see look like surrounded by a halo of the thriller substance.
Nevertheless it’s known as dark matter as a result of it doesn’t give off gentle, or take up or mirror it, which makes it extremely troublesome to detect.
So what’s these things? We expect it should be some form of unknown basic particle, however past that we’re unsure. All makes an attempt to detect dark matter particles in laboratory experiments up to now have failed. Physicists have been debating its nature for many years.
Scientists have proposed two main hypothetical candidates for dark matter. One risk is a comparatively heavy character known as weakly interacting huge particles (or WIMPs). And the opposite risk is that of extraordinarily light-weight particles known as axions. In concept, WIMPs would behave like discrete particles. In the meantime, axions would behave much more like waves because of quantum interference.
It’s been troublesome to tell apart between these two prospects. However now, gentle bent round distant galaxies has provided a clue.
Gravitational lensing and Einstein rings
When gentle touring by way of the universe passes a large object like a galaxy, its path is bent. It bends as a result of – in line with Albert Einstein’s theory of general relativity – the gravity of the large object distorts space and time round itself.
So, generally once we have a look at a distant galaxy we are able to see distorted photographs of different galaxies behind it. And if issues line up completely, the sunshine from the background galaxy shall be smeared out right into a circle across the nearer galaxy.
This distortion of sunshine is gravitational lensing. And the circles it may create are Einstein rings.
By finding out the distortion of the rings or different lensed photographs, astronomers can be taught in regards to the properties of the dark-matter halo surrounding the nearer galaxy.
Axions vs WIMPs
And that’s precisely what Amruth and his group have finished of their new examine. They checked out a number of programs the place a number of copies of the identical background object appeared across the foreground lensing galaxy, with a particular give attention to HS 0810+2554.
Utilizing detailed modeling, they labored out how the pictures could be distorted if dark matter had been made from WIMPs versus axions. The WIMP mannequin didn’t look very like the actual factor, however the axion mannequin precisely reproduced all options of the system.
The consequence suggests axions are a extra possible candidate for dark matter. And their capacity to elucidate lensing anomalies and different astrophysical observations has scientists buzzing with pleasure.
Particles and galaxies
The brand new analysis builds on earlier research which have additionally pointed towards axions because the extra possible type of dark matter. For instance, one study regarded on the results of axion dark matter on the cosmic microwave background. And another examined the conduct of dark matter in dwarf galaxies.
This analysis gained’t but finish the scientific debate over the character of dark matter. Nevertheless it does open new avenues for testing and experiment. For instance, scientists might use future gravitational lensing observations to probe the wave-like nature of axions and probably measure their mass.
A greater understanding of dark matter may have implications for what we learn about particle physics and the early universe. It might additionally assist us to grasp higher how galaxies type and alter over time.
Rossana Ruggeri, Analysis Fellow in Cosmology, The University of Queensland
This text is republished from The Conversation below a Inventive Commons license. Learn the original article.
Backside line: By finding out Einstein rings, scientists have discovered that axions usually tend to be the type of dark matter than WIMPs.
