Sometime soon, or perhaps as early as tonight, a bright new star could appear in the sky, a nova, a massive stellar explosion. This event will be so bright that we can see it with the naked eye from Earth, says NASA, even though the explosion will take place almost 3,000 light years away.
So we don’t have to be afraid. But we can be fascinated. “This is a unique event that will produce many new astronomers,” says Rebekah Hounsell, Astrophysikerin am Goddard Space Flight Center der NasaBecause anyone who experiences such an event will never forget it. “It will motivate the next generation of scientists,” Hounsell is sure.
But what is happening in the depths of space? And why do we know it will happen? The answer is simple: we have already seen it. Most recently on February 9, 1946, and before that on May 12, 1866. Other novae may have been discovered in 1217 and 1787, writes the Thuringian State Observatory (TLS) in Tautenburg. And that’s why astronomers are sure that we will see it again in 2024. Some believe that the explosion will happen before the end of summer. So there is not much time left.
What is exploding in space?
The nova will pass on T Coronae Borealis (T CrB for short), a binary star in the constellation Corona Borealis, the Northern Crown. The system is 2,688 light years from Earth and consists of a white dwarf, about the size of Earth, and an old red giant. The dwarf is much heavier and uses its gravitational force to extract hydrogen from the giant. “The strong gravity compresses this atmosphere, which consists mainly of hydrogen, and heats it up,” explains Dr. Veronika Schaffenroth in the blog of the Thuringian State Observatory Tautenburg. “When a critical temperature is reached, uncontrolled hydrogen fusion sets in and the sudden energy production causes the flat atmosphere to be violently ejected into the surrounding space.” That is why we experience a thermonuclear explosion every 80 years. Not comparable to a supernova, in which a dying star explodes and destroys itself, this nova is no less remarkable.
In a nova event, NASA says, the dwarf star stays intact and hurls the accumulated material into space in a blinding flash. This cycle repeats and can last for tens or even hundreds of thousands of years. “There are some recurring novae with very short cycles, but we don’t usually see a repeated outburst very often in a person’s lifetime, and rarely one so relatively close to our own system,” said Hounsell. “It’s incredibly exciting to have a front row seat like this.”
Who is watching?
Thousands of amateur astronomers around the world are probably waiting for the nova. The professionals are also watching closely. In recent months, astronomers at the Thuringian State Observatory have observed an intensification of the so-called Hα spectral line. “This emission line is caused by the accretion disk around the white dwarf and its strength is linked to the mass accretion rate. In recent months, this line has become stronger again, which suggests that accretion is increasing,” writes TLS researcher Veronika Schaffenroth. Accretion is the accumulation of mass around a cosmic object and the Hα spectral line stands for hydrogen. We remember: The white dwarf collects hydrogen from its companion until there is enough for an explosion.
Where can I see this?
Now, at the end of summer, the constellation is in the west in the early evening. T CrB, the nova double star, is located to the left of the actual crown, not far from Epsilon Coronae Borealis. It can normally only be seen with a telescope. When it goes nova, it will reach a brightness of up to 2 mag, making it as bright as Gemma (α Coronae Borealis), the brightest star in the Corona Borealis. The Pole Star is also comparable.
It will probably be visible to the naked eye for several days, then its brightness will decrease again. It could be visible with binoculars for a few more days, then only with a telescope. And that’s how it will stay – for the next 80 years.
