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Astonishing Discoveries Unveiled at the Heart of the Milky Way

The core of the Milky Way has always been a strange and enigmatic place, but in 2020, astronomers stumbled upon six extraordinary objects orbiting around Sagittarius A*. These peculiar entities defy classification within the known structures of our galaxy, leading astronomers to designate them as a completely new class of objects known as G objects.

The initial pair of objects, named G1 and G2, initially captured the attention of astronomers nearly two decades ago. Over the years, researchers have meticulously studied their orbits and peculiar characteristics. Initially believed to be massive gas clouds spanning 100 astronomical units and elongating as they approached the black hole, these objects exhibited emission spectra consistent with gas and dust.

However, G1 and G2 were not behaving like ordinary gas clouds.

Physicist and astronomer Andrea Ghez from the University of California, Los Angeles, remarked in 2020, “These objects appear to be gas clouds but exhibit star-like behaviors.” Building upon decades of observations of the galactic center, Ghez and her team, led by UCLA astronomer Anna Ciurlo, identified an additional four objects with similar properties: G3, G4, G5, and G6.

The G objects, including G1 and G2 depicted above, exhibit highly diverse orbits distinct from one another. Collectively, their orbital periods span a wide range, varying from 170 years to 1,600 years.

While their exact nature remains elusive, an important clue about these enigmatic objects emerged during G2’s intact emergence from periapsis in 2014. Periapsis refers to the point in an orbit that is closest to the black hole.

“When G2 reached its closest approach, it displayed a remarkably peculiar signature,” explained Ghez. “We had observed it previously, but it didn’t appear particularly unusual until it approached the vicinity of the black hole. At that point, it became elongated, experiencing significant gas disruption. It transformed from a relatively unremarkable object when it was far from the black hole into one that became highly stretched and distorted during its closest approach. It lost its outer shell and is now gradually returning to a more compact state.”

Initially, G2 was believed to be a cloud of hydrogen gas that was anticipated to be torn apart and consumed by Sgr A*, resulting in impressive accretion events. However, nothing noteworthy occurred, leading to the term “cosmic fizzle” to describe the lack of significant activity.

According to the astronomers, the explanation for these peculiar objects lies in the presence of massive binary stars. Typically, these binary systems remain in a stable orbit, functioning as companion stars. However, similar to the merging of binary black holes, these binary stars can collide and merge, forming a single, larger star.

During such mergers, an extensive cloud of dust and gas is generated, encompassing the newly formed star for approximately one million years following the collision.

“There must be something that kept G2 compact and allowed it to survive its encounter with the black hole,” Ciurlo stated. “This provides evidence for the existence of a stellar object within G2.”

As for the other five objects, they could also be the result of binary star mergers. Given the prevalence of massive binary stars in the galactic center and the significant gravitational forces exerted by Sgr A*, it is plausible that their binary orbits are frequently destabilized.

“The merging of stars may be more common in the Universe than previously believed, and it is likely a widespread occurrence,” Ghez explained. “Black holes may be causing binary stars to merge. Many of the stars we have observed, which have been enigmatic until now, may actually be the outcome of these calm mergers. We are gaining insights into the evolution of galaxies and black holes. The interaction between binary stars and the black hole is distinct from that of single stars interacting with other single stars and with the black hole.”

Despite the similarities observed among the G objects, there is still much to uncover. Further expanding the dataset will provide additional information to unravel this intriguing puzzle. Additionally, the occurrence of mysterious flares originating from Sgr A* raises questions. Could it be a delayed reaction from G2’s periapsis? Perhaps the cosmic fizzle was not as lackluster as initially thought. Continued observation of this peculiar corner of space, occupied by the supermassive black hole, will be necessary to unveil what unfolds next.

The research was published in Nature.

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