Hunting down dark matter in a nearby galaxy
doi:10.1038/nindia.2019.47 Published online 16 April 2019
Microlensing is a cosmic process in which a small massive object, acting like a lens, bends light rays travelling from a star towards the Earth. Since the microlensing effect depends only on lens mass, it can be used to search for very faint or invisible objects, such as brown dwarfs, neutron stars, old white dwarfs or black holes, that might make up dark matter.
Using a large digital camera, astrophysicists have searched for microlensing phenomena to detect massive objects such as primordial black holes in the Andromeda galaxy, a spiral galaxy 2.5 million light-years away from Earth1.
The researchers, including a scientist from the Inter-University Centre for Astronomy and Astrophysics in Pune, India, aimed to locate such black holes because they are prime candidates for dark matter, the invisible stuff that constitutes much of the universe. Dark matter doesn’t emit light and is not composed of atoms or their usual constituents such as electrons and protons.
The camera, with a number of sophisticated detectors, monitored tens of millions of stars, particularly in the halo regions of the galaxy that consist mostly of gas. It was able to detect a single black hole candidate.
The researchers say that they can detect more black holes with heavier masses by monitoring the galaxy over longer timescales, from months to years.
Repeated observations of the neigbouring galaxy every few months over years – for example, 10 minutes of monitoring during each observation – would be able to detect black holes 10 times as heavy as the Sun, they add.
1. Niikura, H. et al. Microlensing constraints on primordial black holes with Subaru/HSC Andromeda observations. Nat. Astron. (2019) doi: 10.1038/s41550-019-0723-1