Astronomers expect a “new star” to appear in the night sky anytime between now and September in a celestial event that NASA says has been years in the making.
“It’s a once-in-a-lifetime event that will create lots of new astronomers and give young people a cosmic event to observe for themselves, ask their own questions and collect their own data,” said Dr. Rebekah Hounsell, associate scientist specializing in nova events at NASA’s Goddard Space Flight Center in Greenbelt, Md., said in a statement. “It will drive the next generation of scientists.”
The expected brightening, known as a nova, will occur in the constellation Corona Borealis, or Northern Crown, in the Milky Way, located between the constellations Boötes and Hercules.
While a supernova is the explosive death of a massive star, a nova refers to a sudden, brief explosion from a collapsed star known as a white dwarf. The dwarf star remains intact and releases material in a repeating cycle that can take thousands of years.
“There are a few recurring novae with very short cycles, but we don’t usually see repeated flares very often in human lifetimes, and rarely ones that are relatively close to our own system,” Hounsell said. “It’s incredibly exciting to have this front row seat.”
T Coronae Borealis, otherwise known as the “Blaze Star”, is a binary system in Corona Borealis that includes a dead white dwarf and an aging red giant. Red giants form when stars run out of hydrogen for nuclear fusion and begin to die. In about 5 billion or 6 billion years, our Sun will become a red giant, inflating and expanding as it sheds layers of material and likely vaporizes the inner planets of the solar system, though Earth’s fate remains unclear, according to NASA.
Every 80 years or so, T Coronae Borealis experiences an explosive event.
The stars in the orbiting pair are close enough to each other that they interact violently. A red giant becomes increasingly unstable over time as it heats up, shedding its outer layers, which land as matter on the white dwarf star.
The mass exchange causes the white dwarf’s atmosphere to gradually heat up until a “runaway thermonuclear reaction” occurs, leading to a nova, as seen in the animation below, according to the space agency.
Watching the changing sky
In the fall of 1217, a nova was being released from T Coronae Borealis when a man named Burchard, an abbot of Ursberg, Germany, noticed a “faint star that shone with great light for some time,” according to NASA. This was the first recorded sighting of the Blaze Star.
T Coronae Borealis last experienced an explosive flare in 1946, and astronomers are once again keeping a close eye on the star system.
“Most novae happen unexpectedly, without warning,” William J. Cooke, head of NASA’s Meteoroid Environments Office, said in an email. “However, T Coronae Borealis is one of 10 recurring novae in the galaxy. We know from the last eruption in 1946 that the star will be fainter than a year before rapidly increasing in brightness. T Coronae Borealis began to dim in March.” from last year, so some researchers expect it to be a nova between now and September, but the uncertainty about when that will happen is several months – it can’t be done better with what we know now.”
Located 3,000 light-years from Earth and usually too faint to be seen with the naked eye, the star system is expected to reach a brightness level similar to that of the North Star, or Polaris.
Once the nova reaches peak brightness, it will be like a new star has appeared—one that is visible for a few days without any equipment and a little over a week with a telescope before it dims and disappears from view for the next 80 years or so.
The nova will appear in a small arc between the constellations Boötes and Hercules and will be visible from the Northern Hemisphere.
“The northern corona is a horseshoe-shaped curve of stars west of the constellation Hercules, ideally visible on clear nights,” said a news release shared by NASA. “It can be identified by locating the two brightest stars in the northern hemisphere—Arcturus and Vega—and tracing a straight line from one to the other that takes sky watchers to Hercules and Corona Borealis.”
Sightings around the world
The event promises to be exciting for amateur astronomers, said Dr. Elizabeth Hays, head of the Astroparticle Physics Laboratory at NASA Goddard.
“Citizen scientists and space enthusiasts are always looking for those strong, clear signals that identify nova events and other phenomena,” Hays said. “With social media and email, they send instant alerts and the flag goes up. We look forward to this global community interaction with T CrB again.”
Astronomers will observe the nova with a range of ground-based and space-based telescopes, and data from citizen scientists could help astronomers piece together what happened before the eruption, Hounsell said.
Nova events are usually so distant and faint that it’s difficult to identify the full picture of the eruption, but “this eruption will be really close, there will be a lot of eyes on it,” Hays said.
“Studying recurrent novae such as T Coronae Borealis helps us understand mass transfer between stars in these systems and provides insight into the thermonuclear escape that occurs on the surface of a white dwarf when a star goes nova,” Cooke said.
Cooke recalled that the last nova he witnessed—Nova Cygni in 1975—was similar in brightness to that expected from T Coronae Borealis. Nova Cygni is not expected to experience another outburst again.
“I was a teenage astronomy geek about to start college and I was out on the night of August 29,” Cooke said. “When I looked at the sky, I noticed that the Cygnus constellation was confused; there was a star that shouldn’t be there. After enduring several comments from friends who thought I was crazy, I made them, to look and realize that We were looking at a nova. It was a very memorable experience and reinforced my choice of astronomy as a career. I used to joke that the star had to explode in order to get a degree in physics.
While it’s possible that T Coronae Borealis won’t explode until September, astronomers plan to monitor it just in case.
“Recurring novae are unpredictable and contradictory,” said Dr. Koji Mukai, an astrophysics researcher at NASA Goddard, in a statement. “Just when you think there can be no reason why they follow a certain set pattern, they do – and once you start relying on them repeating the same pattern, they completely deviate from it. We’ll see how T CrB behaves.”