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Unprecedented Observations of Supermassive Black Hole 1ES 1927+654

A particular supermassive black hole has recently become a focal point for astronomers, drawing their attention with a series of extraordinary events. After an unexpected disappearance, it is now showcasing a remarkable spinning phenomenon.

The black hole in focus is known as 1ES 1927+654, which boasts a mass equivalent to one million suns and resides in a galaxy located approximately 100 million light-years from Earth. In 2018, a team from MIT and affiliated institutions made a groundbreaking observation when the corona surrounding the black hole—a halo of rapidly moving, superheated plasma—suddenly vanished, only to reconstitute itself several months later. This event marked a first in the realm of black hole studies.

Now, astronomers from the MIT team have documented even more unusual behavior from the same black hole, detecting an escalated frequency of X-ray flashes. Over a two-year span, the cadence of these flashes transitioned from occurring every 18 minutes to every seven minutes. Such a significant increase in X-ray activity has not been previously recorded for a black hole.

The researchers have considered several hypotheses to explain this newfound activity, concluding that a rotating white dwarf might be the likely source. This compact remnant of a star is thought to be orbiting the black hole and inching closer to its event horizon, the point beyond which nothing can escape the black hole’s gravitational grip. If accurate, this scenario suggests the white dwarf is maintaining a precarious balancing act, skirting around the black hole’s edge without succumbing to its pull.

“This would represent the closest object we know of near any black hole,” explained Megan Masterson, a graduate student in physics at MIT and co-author of the study. “This suggests that white dwarfs can survive remarkably close to an event horizon for substantial periods of time.”

The findings will be presented at the 245th meeting of the American Astronomical Society in National Harbor, Maryland.

Should a white dwarf indeed be responsible for the black hole’s X-ray emissions, it is expected to produce gravitational waves, detectable by advanced observatories like NASA’s upcoming Laser Interferometer Space Antenna (LISA).

“These next-generation detectors are tailored for picking up oscillations that occur over minutes, perfectly aligning with the behavior of this black hole system,” noted co-author Erin Kara, an associate professor of physics at MIT.

Atypical Behavior

Kara and Masterson were part of the team that monitored 1ES 1927+654 back in 2018 as the black hole’s corona faded and gradually reformed. At one point, the reconstituted corona became the brightest source of X-ray emissions in the cosmos.

“Although it maintained a high brightness, it displayed no new activities for a couple of years and was somewhat stagnant. We knew we had to keep observing because it was incredibly captivating,” Kara remarked. “Then we discovered something that had not been seen before.”

In 2022, the team revisited data obtained from the European Space Agency’s XMM-Newton satellite, which specializes in X-ray astronomy. They found that the black hole was emitting X-rays that pulsed with a progressively increasing rate. Such “quasi-periodic oscillations” have only been observed in a limited number of supermassive black holes where X-ray emissions occur in a rhythmically consistent pattern.

For 1ES 1927+654, the intervals between emissions seemed to tighten, dropping from every 18 minutes to just seven within two years.

“We’ve never witnessed such rapid changes in the emission frequency,” Masterson commented. “It was entirely different from any typical black hole behavior.”

The identification of X-ray emissions suggests the source is situated very near the black hole, likely within a few million miles of the event horizon. In regions close to a black hole, conditions are extreme, resulting in the generation of X-rays by high-velocity, heated plasma. Emissions from further out are typically in the optical and ultraviolet spectra, as the cooler gas in an accretion disk does not emit X-rays.

“Detection of X-rays indicates proximity to the black hole,” Kara explained. “When variability occurs on a minute timescale, it points to interactions near the event horizon, leading us to consider the possibility of objects orbiting around the black hole.”

Increasing X-ray Activity

The phenomenon responsible for the X-ray emissions is believed to occur at a remarkably close distance to the black hole, within millions of miles of the event horizon. Masterson and Kara investigated various astrophysical models to elucidate the observed X-ray patterns, including one involving oscillations of the black hole’s corona.

“One theory suggests that the corona could be fluctuating, potentially changing in size and leading to faster oscillation rates as it contracts,” Masterson noted. “However, we are just beginning to comprehend the dynamics of coronal oscillations.”

A more plausible explanation centers around the interacting white dwarf. “These stars are quite dense and compact, and we hypothesize that the white dwarf is approaching very closely to the black hole,” Masterson elaborated.

The researchers estimate the white dwarf’s mass to be around one-tenth that of the sun, compared to the supermassive black hole’s mass, which is about one million times greater than that of our sun.

When celestial bodies venture close to a supermassive black hole, they experience gravitational wave emissions, which draw the object in. As the white dwarf orbits nearer, it accelerates, which can account for the observed uptick in the frequency of the X-ray oscillations.

The white dwarf is reportedly nestled close to the edge of the event horizon yet is not expected to fall in. While the black hole’s gravity exerts a pull, it is also pulling material from the white dwarf, which creates opposing forces that may allow the star to persist just outside the gravitational point of no return.

“Because of their density, white dwarfs are difficult to disintegrate, allowing them to maintain proximity to the black hole,” Kara said. “If our hypothesis holds, we may observe the white dwarf oscillating around this critical boundary.”

The research team intends to persist with their observations using current and future telescopes to deepen their understanding of the extreme conditions present near a black hole. They are particularly eager to investigate further when LISA, the space-based gravitational-wave detector, is scheduled to launch in the mid-2030s, as it will be capable of detecting the gravitational waves produced by this intriguing system.

“This source has taught us to remain vigilant in our observations, as it continues to reveal new insights,” Masterson concluded. “Our next objective is simply to keep observing.”

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