Pulsars set first mass limits on supermassive black hole pairs in the early universe
So far, observations by instruments including the James Webb Space Telescope have revealed the presence of surprisingly massive black holes in the early universe. Even less than a billion years after the Big Bang, some of these bodies already weighed billions of times the mass of the sun, and to date, astronomers are unclear as to how they could have grown so large so quickly.
Recent observations of massive black holes in the early universe have baffled astronomers, who are unsure how these entities could have grown so swiftly within a billion years post the Big Bang. A new study published in Physical Review Letters by researchers from Beijing Normal University has unveiled the first direct mass limits on pairs of supermassive black holes from the epoch known as the cosmic dawn.
These black holes, when in orbital motion, create gravitational waves that stretch across the cosmos. However, as they travel from their source to Earth, these waves are affected by the universe's expansion, which could lead to inaccuracies in estimating the masses of distant pairs. This study overcame this issue by incorporating the significant redshift in signals originating from the early universe, demonstrating that brightening waves can counteract their dimming due to distance.
The researchers analyzed a decade's worth of data from 30 pulsars within the Parkes Pulsar Timing Array in Australia, combining their findings with the known positions and redshifts of two distinct targets. One target was an extremely luminous quasar detected less than 900 million years post the Big Bang, while the other was one of the farthest galaxies ever identified by the James Webb Space Telescope, observed under 300 million years post the Big Bang.
Through this analysis, the team established upper limits on the masses of black hole pairs in these systems, ruling out pairs exceeding 10 billion solar masses for both targets. This marks the first time gravitational-wave constraints have been applied to black hole pairs during the cosmic dawn. As more data becomes available from various pulsar timing arrays, and as future facilities like the Square Kilometer Array enhance their capabilities, the researchers anticipate that these mass limits will become even more precise.
This breakthrough offers promising insights into the detection of less extreme black hole pairs using dedicated searches and complements observations of short gravitational-wave bursts. By demonstrating that distance is not a definitive barrier to detecting black hole pairs, this study opens up a new avenue for astronomers to explore these massive entities and potentially explain their rapid growth in the early universe.
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