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The Blue Ring Nebula has puzzled scientists for the past 16 years. Discovered in 2004, the colorful nebula has defied scientists’ attempts to reconstruct its origin story.
But a team of astronomers may have finally solved the case. In a new study, they suggest that this large blue patch of gas with a star in the center is actually debris left over from the merger of two stars thousands of years ago.
Their findings are detailed in a study published Wednesday in the journal Nature.
The Blue Ring Nebula was first spotted in 2004 by NASA’s space telescope, the Galaxy Evolution Explorer (GALEX). The Nebula looked like nothing scientists had seen before: it looked like a large gas patch with a star in the middle. Although it appears blue in scientists’ images of the nebula, it does not actually emit colors that can be seen by the human eye. Rather, its invisible ultraviolet light was blue-coded from the telescope images.
The Blue Ring Nebula is the same size as the faint remnant of a supernova explosion – the aftermath of a large star running out of fuel and extinguishing in explosive death. But this nebula has a living star in the center. And so began the hunt for the truth behind this strange object.
A history of violence – In 2006, scientists observed the nebula using two powerful telescopes: the Hale telescope at the Palomar Observatory in San Diego County, California, and the WM Keck Observatory in Hawaii. In their observation, they found eloquent evidence of a shock wave around the nebula, indicating that some sort of violent event had occurred there, ejecting the nebula’s gas into space.
“For quite a long time we thought that maybe there was a planet several times the mass of Jupiter torn apart by the star, and that was throwing all that gas out of the system,” Mark Seibert, an astrophysicist at the Carnegie Institution for Science and a member of the GALEX team said in a statement.
The mystery lasted. In 2012, the same team of scientists identified a disk of dust in a tight orbit around the star. The size of the disc suggested that it came from an object much larger than a planet, ruling out the scientists’ previous hypothesis.
The evidence began to grow. The team collected data from four space telescopes, four ground-based telescopes and historical observations of the star dating back to 1895. Armed with this enormous treasure trove of information, they dived again, determined to solve the mystery once and for all.
Their forensic approach appears to have paid off. Hidden in the data, they uncovered evidence suggesting that the Blue Ring Nebula is actually the result of merging two stars, one the same size as our Sun and another about one-tenth that size.
How did it happen? – Thousands of years ago, towards the end of its life cycle, the Sun-sized star began to swell. As he did so, he came a little closer to a smaller and closer star. Due to the gravitational pull of the large star, the smaller star fell in a downward spiral towards its larger companion.
Over time, the larger star began tearing apart its smaller counterpart and enveloped itself in a ring of debris before completely swallowing the smaller star.
Their merger triggered a cloud of hot debris, ejected into space and cut in half by the disc of gas in the center. As a result, two cone-shaped clouds of debris formed, moving in opposite directions, with one cone traveling towards Earth and the other directly away from our planet. Although the individual cones are too faint to spot on their own, the area where they overlap is what forms the shape of the Blue Ring Nebula.
“We see many two-star systems that might one day merge and we think we have identified stars that merged perhaps millions of years ago. But we have almost no data on what happens in between,” Brian Metzger, associate professor of astronomy at Columbia University and co-author of the study said in a statement.
“We think there are probably many young remnants of stellar mergers in our galaxy, and the Blue Ring Nebula could show us what they are like so we can identify more of them.”
Abstract: Stellar mergers are a short but common phase in the evolution of binary star systems1.2. These events have many astrophysical implications; for example, they can lead to the creation of atypical stars (such as magnetic stars3, blue stragglers4 and rapid rotators5) play an important role in our interpretation of stellar populations6 and represent the channels of formation of the mergers of compact objects7. Although a handful of stellar mergers have been observed directly8.9, the central remnants of these events were enveloped in an opaque shell of dust and molecules10, making it impossible to observe their final state (for example, as a single united star or a narrower, surviving track11). Here we report observations of an unusual ring-shaped ultraviolet (“blue”) nebula and the star at its center, TYC 2597-735-1. The nebula has two opposite sides, suggesting a bipolar outflow of material from TYC 2597-735-1. The spectrum of TYC 2597-735-1 and its proximity to the galactic plane suggest it is an old star, but it has abnormally low surface gravity and long-term detectable brightness decay, which is unusual for its evolutionary stage. TYC 2597-735-1 also shows Hα emission, radial velocity changes, enhanced ultraviolet radiation and excess infrared emission: signs of dusty circumstellar discs12, stellar activity13 and growth14. Combined with stellar evolution models, the observations suggest TYC 2597-735-1 merged with a lower-mass companion several thousand years ago. TYC 2597-735-1 provides a glimpse into unobstructed stellar fusion in an evolutionary phase between its dynamic inception and theorized final equilibrium state, allowing for direct study of the fusion process.
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