Celebrating Black Holes

Each year, NASA and other organizations pick one week to celebrate one of Nature’s most enigmatic objects, the black hole. To mark the 2022 #blackholeweek, the editors of Physics searched the magazine’s archives to find the most read black hole stories.

The First Sounds of Merging Black Holes

Among the most read Physics stories—on any topic—is that on the first detection of gravitational waves emitted by the merger of two black holes. The publication of the observation broke the APS servers as physicists around the world tried to access the Physical Review Letters paper reporting the finding. Emanuele Berti, now at Johns Hopkins University, wrote that the observation sets the course for a new era in observational astronomy.

Read the Viewpoint.

A Lopsided Merger

Gravitational waves were also the subject of a 2020 report of an unexpected observation: the merger of two black holes with remarkably different masses. The gravitational waves from this event were detected during the third observation run of the LIGO and Virgo experiments. In his commentary on the finding, Stephen Taylor of Vanderbilt University wrote that the detection opened a trove of new scientific possibilities, ranging from constraining black hole spins to testing Einstein’s theory of general relativity in previously unexplored regimes.

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A Heavyweight Merger

A month after the report of the lopsided merger, the LIGO and Virgo collaborations announced that they had detected the heaviest black hole merger to date. In this merger a 65-solar-mass black hole coalesced with an 85-solar-mass black hole to form a 142-solar-mass black hole. In her commentary, Rosalba Perna of Stony Brook University called the observation of a merger involving such unusually large masses “exceptional.”

Read the Viewpoint.

Black Holes Have Soft Quantum Hair

Four decades ago, Stephen Hawking proposed that black holes could destroy information—a conclusion that is incompatible with the standard laws of quantum physics. In this 2016 story, Gary Horowitz of the University of California, Santa Barbara, discussed a new study by Hawking and others suggesting a possible idea for solving this paradox: instead of destroying information, black holes might release it through so-called soft hair.

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Illuminating Black Holes through Turbulent Heating

A black hole becomes visible to astronomers when its encircling plasma falls inward, causing this ionized gas to heat up and emit radiation. But those heating mechanisms remain unidentified. Gregory Howes of the University of Iowa wrote about predictions suggesting that it should be possible to observationally distinguish the mechanisms governing this heating.

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Supermassive Black Hole May Constrain Superlight Dark Matter

In April 2019, astronomers presented the first image of a black hole, taken by the Event Horizon Telescope. In a commentary, Eric Armengaud of the University of Paris-Saclay discussed how that image was being used to place new bounds on the mass of a type of dark matter known as fuzzy dark matter.

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Black Hole Imaging Test Einstein’s Limits

As well as acting as a probe for dark matter, the images and future movies from the Event Horizon Telescope could help theorists answer one of the biggest open problems in physics: why general relativity and quantum mechanics produce conflicting predictions. “There are all these exciting theoretical puzzles that make black holes interesting to theorists,” said Alex Lupsasca of Harvard University in this feature article. Gravitational-wave detectors and the EHT have transformed the field so much that it’s “suddenly an experimental science,” he added.

Read the News Feature.

Nobel Prize: Facing the Reality of Black Holes

Albert Einstein had doubts that black holes might exist, suggesting that, while these objects are predicted by his theory of general relativity, they may not occur in the real world. But the recent observations have made the reality of black holes inescapable. The 2020 Nobel Prize in Physics recognized Roger Penrose, Reinhard Genzel, and Andrea Ghez for their contributions to the field. In this Focus story, Vitor Cardoso from the Technical University of Lisbon, Portugal is quoted as saying that these advances, combined with gravitational wave detections, make for “truly fascinating times for those trying to understand how gravity and the cosmos work.”

Read the Focus Story.

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