T Coronae Borealis: A star is going to explode and will be visible to the naked eye very soon | Science

T Coronae Borealis: A star is going to explode and will be visible to the naked eye very soon | Science
T Coronae Borealis: A star is going to explode and will be visible to the naked eye very soon | Science

Like people, stars are born, grow and die. And they do it in events that cause large explosions. A supernova is the death of a supergiant star, while a nova leaves the stars alive after shining with a sudden, explosive flash. In general, these events can be difficult to predict, but at least 10 white dwarf systems are known to produce novae periodically, five of them in our galaxy. This is the case of T Coronae Borealis (T CrB), located about 3,000 light years from Earth. Its historical observations indicate that it explodes approximately every 80 years and that cycle is close to completion. Once it occurs, it will be observable to the naked eye as a new star in the night sky.

According to NASA, it is very likely that the T CrB two-star system will generate a huge explosion again. The last time was in 1946 and some astronomers had suggested that it will do so again between February and September of this year. However, other experts prefer not to venture to give such a close estimate. Sumner Starrfield, an astronomer at the University of Arizona who has observed the behavior of the nova, explains regarding the date of the long-awaited event: “It could be tonight, this fall, or it could be in 2025 or 2026.

There is no way to determine when it will actually explode. “Our estimates that it will be soon are based on observations of its behavior just before its explosion 80 years ago.” Javier Armentia, astrophysicist and director of the Pamplona Planetarium, agrees not to rush the forecast: “Current behavior gives us clues, but it is not possible to define.”

Every time a new star appears in the sky, it is called not going –new, in Latin—; although in reality it is an astronomical event that causes an explosive flash of a star that was already there. T CrB is actually composed of two stars: a red giant and a white dwarf. The second is a dense stellar core whose gravity attracts the red giant’s gas. The gas accumulates on the surface of the dwarf until it explodes in an “extremely violent” event, as described by Armentia. The star temporarily shines more intensely, and reaches the luminous magnitude of the North Star. Eventually, it returns to normal and the cycle repeats.

Seeing this nova is a once in a lifetime opportunity. The size disparity between the two stars is so great that it takes the white dwarf 227 days to orbit its red giant, Starrfield explains. They are so close that matter ejected by the red giant accumulates near the surface of the white dwarf. Once the roughly Earth-sized mass has accumulated in the white dwarf—which takes about 80 years—it becomes hot enough to start a runaway thermonuclear reaction. This causes a huge explosion, because “in a few seconds the temperature increases by 100 to 200 million degrees Celsius,” details this astronomer.

A red giant star and a white dwarf orbit each other in this animation of a nova.NASA Goddard Space Flight Center

A stellar explosion can manifest itself in a very noticeable way in space. Depending on the magnitude and distance, the event can be observed with the naked eye or using homemade telescopes. The T CrB nova will be observable with the naked eye. If what happened in its last explosion is repeated, it will be visible for about a week and the system will return to tranquility in a couple of months: “We will be observing it throughout its evolution,” explains Starrfield.

Novas are rare phenomena, so both astronomers consider it will be a great opportunity to expand knowledge about them. “We don’t know much about novae. “Now we have more advanced data and technology than we had in 1946,” describes Armentia. And according to Starrfield, thanks to the big event it will be possible to learn how much energy is involved in the explosion, how much of that material is ejected into space, what the chemical composition of the gases is and how the big bang occurs.

“Is the gas expelled in a huge cloud? Or in many smaller clouds?” are questions to which Starrfield seeks answers. He is optimistic and assures that there will be more information “that will surprise us.” Thanks to the observation of novae, explains Starrfield, indications have been found that part of the material from which the solar system was formed could have been produced in nova explosions. “We are pretty sure that the lithium in the solar system comes from nova explosions that occurred before the formation of the solar system,” he explains. Normal novae explode “perhaps every 100,000 years,” he adds. But recurring novae repeat their bursts in a human span due to a peculiar relationship between their two stars.

A conceptual image of how to find T Coronae Borealis.POT

It is at least the third time that humanity has witnessed the T CrB nova, officially discovered by the Irishman John Birmingham in 1866, and then when it reappeared in 1946. While waiting for it to make a big explosion again, astronomers invite to become familiar with the constellation of the Corona Borealis, or Northern Crown, which is a small semicircular arc between the star Arthur—one of the brightest and easiest to locate—and the constellation of Hercules. “That is where the burst will appear as a bright new star,” explain NASA specialists.

Starrfield’s team has booked time at the space telescope James Webb to observe the eruption, but this will be just one of many eyes turned toward the outbreak once it begins. Such advanced technology is not necessary to witness this extraordinary event once it occurs. The star will be visible to the naked eye for about a week; and with binoculars, for a month. You just need to go out and look at the Corona Borealis constellation.

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