Physicists have been puzzling over conflicting observational results pertaining to the accelerating expansion rate of our Universe—a major discovery recognized by the 2011 Nobel Prize in Physics. New observational data from the James Webb Space Telescope (JWST) has confirmed that prior measurements of distances between nearby stars and galaxies made by the Hubble Space Telescope are not in error, according to a new paper published in The Astrophysical Journal. That means the discrepancy between observation and our current theoretical model of the Universe is more likely to be due to new physics.

As previously reported, the Hubble Constant is a measure of the Universe's expansion expressed in units of kilometers per second per megaparsec (Mpc). So, each second, every megaparsec of the Universe expands by a certain number of kilometers. Another way to think of this is in terms of a relatively stationary object a megaparsec away: Each second, it gets a number of kilometers more distant.

How many kilometers? That's the problem here. There are basically three methods scientists use to measure the Hubble Constant: looking at nearby objects to see how fast they are moving, gravitational waves produced by colliding black holes or neutron stars, and measuring tiny deviations in the afterglow of the Big Bang known as the Cosmic Microwave Background (CMB). However, the various methods have come up with different values. For instance, tracking distant supernovae produced a value of 73 km/s Mpc, while measurements of the CMB using the Planck satellite produced a value of 67 km/s Mpc.

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© NASA/ESA/CSA/STScI/A. Riess (JHU)

What happens when a gargantuan cloud of gas swallows a pair of monster black holes with their own appetites? Feasting on the gas can cause some weird (heavenly) bodily functions.

AT 2021hdr is a binary supermassive black hole (BSMBH) system in the center of a galaxy 1 billion light-years away, in the Cygnus constellation. In 2021, researchers observing it using NASA’s Zwicky Transient Facility saw strange outbursts that were flagged by the ALerCE (Automatic Learning for the Rapid Classification of Events) team.

This active galactic nucleus (AGN) flared so brightly that AT 2021hdr was almost mistaken for a supernova. Repeating flares soon ruled that out. When the researchers questioned whether they might be looking at a tidal disruption event—a star being torn to shreds by the black holes—something was still not making sense. They then compared observations they made in 2022 using NASA’s Neil Gehrels Swift Observatory to simulations of something else they suspected: a tidal disruption of a gas cloud by binary supermassive black holes. It seemed they had found the most likely answer.

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© Northwestern University

The giant holes in galaxies’ centers shouldn’t be able to combine, yet combine they do. Scientists suggest that an unusual form of dark matter may be the solution.