Mysterious Streak of Stars Might Be a Flat Galaxy and Not a Runaway Black Hole, New Study Suggests

Last month, astronomers made headlines when they reported the existence of a rogue black hole, estimated to be as massive as 20 million suns, based on observations from the Hubble Space Telescope. The most intriguing aspect was the extensive trail of stars trailing behind the black hole as it rapidly moved away from its host galaxy.

However, a new study has presented a different perspective on the matter, leaving astronomers in a state of uncertainty. The enigmatic stream of stars resembling a colossal cosmic river might not be caused by a rogue black hole after all, but rather by a peculiarly flat galaxy. This alternative explanation is now being put forward, but the mystery surrounding this phenomenon remains unresolved.

The Flat Galaxy Hypothesis

A team of researchers from the Instituto de Astrofisica de Canarias (IAC) has proposed an alternative explanation for the observed trail of stars, Space.com reported. They suggest that it could be a flat disk galaxy seen edge-on, a common type of galaxy in the universe. The size, motion, and abundance of stars in the observed structure align with what is typically observed in local disk galaxies.

To support their interpretation, the team compared the characteristics of the starry trail to those of a well-studied bulge-less galaxy named IC5249, which is similar in mass to the observed "tail" of stars.

Researchers said in a news release via EurekAlert! that the comparison between the two objects revealed remarkable similarities in their observations and velocity patterns, further supporting the idea that the trail of stars is a galaxy behaving like a galaxy.

The team's analysis of the relationship between the mass of the presumed flat galaxy and the maximum velocity of its rotation strengthened their conclusion.

Despite the resolution of the mystery, the object remains interesting due to its large size and a considerable distance from Earth compared to the majority of galaxies.

The research, titled "Supermassive Black Hole Wake or Bulgeless Edge-on Galaxy?" conducted by the team, has been accepted for publication in the journal Astronomy and Astrophysics.

Researchers of the Runaway Blackhole Hypothesis Not Convinced

Pieter van Dokkum, the lead author of the initial paper proposing the runaway black hole hypothesis, remains skeptical of the new interpretation. In an email to Live Science, he pointed out inconsistencies between the streak observations and the galaxy hypothesis.

For example, far-ultraviolet observations reveal a direct connection between the stellar stream and a nearby compact galaxy, indicating the involvement of a fast-moving object like a supermassive black hole. The presence of a bright knot of ionized gas at the leading edge of the streak further supports the black hole theory but is not accounted for in the edge-on galaxy explanation.

The size of the streak is also atypical for a galaxy located so far from Earth, as acknowledged by the IAC team. Van Dokkum stated that while other explanations are possible, an edge-on galaxy can be largely ruled out based on the available evidence.

Regardless of the true explanation, further study of this intriguing stellar trail is warranted. Additional Hubble observations scheduled for the summer are expected to provide more definitive insights into the galaxy hypothesis. The James Webb Space Telescope has been chosen to observe the mysterious streak, aiming to gather direct evidence of black holes in the region.

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