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An artist’s fanciful impression of tiny primordial black holes. Credit: NASA’s Goddard Space Flight Center.
Hunting for tiny black holes from the dawn of time
Hunting for tiny black holes from the dawn of time
Most of the matter in the Universe is invisible “dark matter”, and nobody knows what it is. One idea is that it is made of tiny black holes formed just after the Big Bang. Daksha’s two satellites, looking at the same gamma-ray bursts from different places, offer a new way to search for them.
For astronomers: technical details
For astronomers: technical details
Primordial black holes in the 10⁻¹⁵–10⁻¹¹ M☉ window remain largely unconstrained. Their Schwarzschild radii are smaller than optical wavelengths, which suppresses optical microlensing, but lensing of hard X-rays still applies. Parallax between the two satellites produces different magnifications of the same GRB. If all dark matter were PBHs of 10⁻¹⁵–10⁻¹² M☉, the probability of Daksha detecting lensing ranges from ~16% to ~6% for 1000 jointly detected GRBs (~80% to ~50% for 10,000), so non-detections alone are not conclusive; pairing with a GRB detector at lunar distances is far more powerful. See Gawade et al. 2023 (MNRAS 527, 3306) and Bhalerao et al. 2024, Science with the Daksha High Energy Transients Mission (Experimental Astronomy 57, 23), section “Primordial black hole abundance”. All Daksha papers are listed on our Publications page.
The dark matter puzzle
The dark matter puzzle
Stars and galaxies move as if they are held together by far more matter than we can see. This invisible “dark matter” outweighs ordinary matter by about five to one, but what it is remains one of the biggest open questions in science. Most searches look for new kinds of subatomic particles — so far without success.
Primordial black holes
Primordial black holes
Another possibility is that dark matter is made of black holes that formed in the first fraction of a second after the Big Bang, long before any stars existed. These primordial black holes could have a huge range of masses. Observations have ruled out most of them, but one window remains open: black holes about as massive as an asteroid, yet each far smaller than a grain of sand. In this range, they could make up all of the dark matter.
A cosmic magnifying glass, seen from two places
A cosmic magnifying glass, seen from two places
Gravity bends light. If a tiny black hole passes very close to our line of sight to a gamma-ray burst, it can act like a magnifying glass and change how bright the burst looks. Daksha’s two satellites, on opposite sides of the Earth, are about 14,000 km apart, so they view each burst along slightly different lines of sight. A tiny black hole could brighten the burst for one satellite but not the other. Comparing the two satellites’ measurements is a new way to search for these objects — something no single satellite can do.
Visible light is no use here: its waves are too long to be focused by such tiny black holes. X-rays and gamma rays have far shorter waves, which is why Daksha can make this search. Daksha will begin it; combined with a future detector much further from Earth, the same method could settle whether such black holes make up the dark matter.
Support Daksha
Support Daksha
If you would like to see Daksha fly, please take a minute to fill in our short support form. Every response helps show the scientific community’s interest in the mission.
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