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In 2004, astronomers identified a unique celestial feature that, when viewed in ultraviolet, looked like a bright eye staring directly at the Earth. Unbeknownst to them, it would take 16 years to figure out what caused the formation of the Blue Ring Nebula.
The Blue Ring Nebula is the remnant of two merging stars, according to new research published today in Nature.
The bright yellow dot in the center of the feature is the surviving stellar remnant (the merger of two stars); the blue ring is an expanding cloud of debris that interacts with the stellar medium; and the magenta outline is the leading edge of the shock wave. To be clear, the blue and magenta colors seen in the nebula represent ultraviolet light and cannot actually be seen with the naked eye.
Colliding stars are always sighted, so this discovery may not seem very special or exciting. What’s special about all of this, however, is the timing of our observations, as astronomers are witnessing this stellar merger some 5,000 years after it happened (not including the time it took for light to reach Earth). Typically, colliding stars are seen immediately after their setback.
“The merging of two stars is quite common, but they are quickly obscured by a lot of dust as the ejection from them expands and cools into space, which means we can’t see what really happened,” explained Keri Hoadley, l lead author of the new study and a physicist at the California Institute of Technology, in a statement. “We think this object represents an advanced stage of these transient events, when the dust finally clears and we have a good view.”
To which he added: “But we also understood the process before it was too long; after time, the nebula will dissolve into the interstellar medium and we would not be able to tell that anything happened. “
Diagram showing what the nebula would look like when viewed from the side. (Graphics: Mark Seibert)
The Blue Ring Nebula, therefore, is not something we have ever seen before and is providing new science. The expanding blue ring, for example, is actually one of a pair. We can’t really see it from our perspective on Earth, but this nebula is actually shaped like two funnels linked together at their points, with the merged star in the center. These rings move away from each other in opposite directions, at speeds reaching 402 kilometers per second (400 kilometers per second). The team calls this a “biconical symmetrical outflow” and provides some important clues as to what happened during the fatal encounter.
Speaking at a press conference on Tuesday, Mark Seibert, co-author and astrophysicist with the Carnegie Institution for Science, said that “everything we’ve learned is interesting” and that the united star “is one of a kind right now.” In fact, this stellar object is a bit strange, as it is surrounded by a disk, the material from which it pours directly into the star.
Diagram showing how we see the feature from Earth. (Graphics: Mark Seibert)
This story began in 2004 when Seibert, while participating in NASA’s Galaxy Evolution Explorer (GALEX) mission, was one of the first to observe the Blue Ring Nebula. At the time, Chris Martin, a co-author of the new study and a physicist from the Caltech thought it “was a really cool thing” and that his team “should have a nice document within the year to explain everything,” As he told reporters yesterday.
This “within the year” document, however, did not have to be, as the nature of the object remained elusive. Data collected by Caltech’s Hale Telescope at the Palomar Observatory and the WM Keck Observatory in Hawaii revealed the presence of a shock wave around the star, hinting at something violent and dramatic. One early hypothesis was that a hot Jupiter-like planet was trapped in a death spiral around the star, and we were witnessing its destruction in the form of a nebula. But the researchers couldn’t be sure, and “ambiguities remained throughout the study,” Martin said.
The scientists also examined the state of the central star, known as TYC 2597-735-1, and found that it was quite old and no longer burned hydrogen in its core. Many other aspects of the object did not match their expectations for the stars. Calling it a “Sherlock Holmes mystery,” Martin said it “became impossible to find a scenario to explain all these observations,” so “after a few years of study, we kept doing other things and the project settled dormant for a while. ‘. “
That changed in 2017 when Hoadley joined Martin’s group as a postdoctoral fellow, and she seemed eager to take the lead in this hibernation project.
“I heard about it on the second day of work and was immediately hooked,” she said at the virtual press conference.
The team had collected a lot of data, but their challenge was to “figure out how to put all the pieces together” and specifically determine what it was like that the nebula glowed in the first place.
As the work progressed, however, the team began to realize that they were not dealing with a planet and that the likely scenario was a stellar collision. The mass of material ejected from the star, for example, was too much for a planet, Hoadley explained. Additionally, data collected by the Habitable Zone Planet Finder on the Hobby-Eberly telescope in Texas found no evidence of a planet within this system.
Things got weirder when the team examined archival data collected by NASA’s Spitzer Space Telescope and Wide-field Survey Explorer (WISE), along with other infrared observatories. These data indicated the presence of an accretion disk around the star. Normally, these dust rings are seen around young stars, but TYC 2597-735-1 is actually quite old.
To make sense of all of this data, the team recruited Columbia University astrophysicist Brian Metzger, an expert on cosmic fusion. Interestingly, Metzger’s mathematical and computational models matched well with his observations of the Blue Ring Nebula.
“It wasn’t just that Brian could explain the data we were seeing; it essentially predicted what we had observed before we saw it, “Hoadley explained in a Caltech press release.” It said, ‘If this is a stellar merger, you should see X’, and it was like, ‘Yes! We see it!’ “
So here’s the story of the Blue Ring Nebula, as revealed in the new document.
Thousands of years ago, a small star orbited a larger star with roughly the same mass as our Sun. As the larger star aged, however, it swelled, expanding to reach very close to its closest companion. small. The smallest star – about one-tenth the size of our Sun – fell in a downward spiral that produced a gas disk. The large star eventually absorbed the smaller star, producing an expanding cloud of debris that was cut in half by the disk. This merger produced the two cone-shaped debris clouds we see today.
Over the thousands of years that followed, the expanding cloud of debris cooled, forming hydrogen molecules that interacted with the stellar medium. Today we see these collisions as brilliant ultraviolet emissions. The cloud is now “dissolving into the interstellar medium” and “we are just trying to capture it as all the exciting particles are present,” Hoadley told reporters.
Hoadley expects the Blue Ring Nebula to last from another thousand to a few tens of thousands of years, after which the feature will disappear completely. It is a real blink of an eye in cosmological terms and a wonderful opportunity to do fascinating science.
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