There are spectacular astronomical events that we can be lucky enough to see more than once in our lives, such as a total eclipse of the Sun or the luminous trace of a superbolide in the night sky, with the permission of the majestic comets. But a much more exceptional event is about to happen in the sky, which may even begin tonight. This is a stellar explosion, a nova, that will be visible to the naked eye.
NASA has announced that this astronomical phenomenon will be able to be observed soon, for several days and with the naked eye.
NASA’s Goddard Space Flight CenterCC BY-SA
A new (and ephemeral) point of light in the sky
This rare but spectacular nova event consists of a sudden increase in luminosity in a certain region of space. From Earth it will look as if a star suddenly appeared. It will appear in the small constellation Corona Borealis, about 3,000 light years from Earth.
Several of the brightest stars in this constellation host planetary systems, including Negolu, a Jupiter-like planet in whose atmosphere water vapor has been detected. It will be in this part of the sky where a new point of light will emerge, the result of a stellar explosion in a binary system formed by a white dwarf star and a red giant.
How and when do these nova-type explosions originate? What will this new object look like in the sky?
A thermonuclear explosion 3,000 light years away
A new star is not forming nor is it a “stellar death” (as occurs in supernova events). The increase in brightness that we will be able to observe will be the result of thermonuclear reactions that are triggered in a binary system of two stars that orbit each other: the T Coronae Borealis (T Cr) system.
One of them is a white dwarf (called T CrB) with a mass similar to the Sun and a diameter about 100 times smaller, a circumstance that causes an intense gravitational field. Its companion star, a red giant T CrA, is losing matter (mainly hydrogen) due to the powerful gravity of T CrB. And hydrogen is progressively deposited on the surface of the white dwarf.
POT
As a consequence, the concentration of hydrogen in the white dwarf rises progressively and there is an increase in pressure and heat until it reaches its limit. It then explodes in a colossal thermonuclear explosion, similar to the detonations of terrestrial fusion bombs.
The dwarf star will return to its original state after this violent episode, it will collect hydrogen from its companion again, and so on until the nova repeats itself in about 80 years. That is why it is so difficult to witness this event twice in a lifetime.
Recurrent or periodic novas
Generally we cannot predict with certainty when such a stellar explosion will occur. However, there is a small group of white dwarf binary systems that generate novae periodically, that is, they repeat in cycles of a few decades. We are talking about recurring or periodic novae and, fortunately, T CrB belongs to this select club.
In addition to knowing the periodicity in which the white dwarf is filled to the limit, researchers have other indications about the imminence of this nova event. Thus, according to NASA scientist William J Cooke, the dimming of a white dwarf during a previous period of one year is a clear sign of the proximity of a stellar explosion. YT CrB began to darken in March 2023.
So what exactly will we see in the night sky, probably one night this summer?
An appearance similar to the North Star
When cataloging bright objects in the sky, such as planets or stars, astronomers use a well-known parameter called apparent magnitude.
Basically, it is related to the brightness of a star as it appears in the night sky and depends on its luminosity and its distance from us. The lower the apparent magnitude value, the brighter the object will be in the sky.
Thus, for example, the apparent magnitude of the full Moon is -12.6, that of the star Sirius (the brightest in the night sky) -1.46, while the North Star gives a value of +2.
The T CrB star system has an apparent magnitude of +10, but when the next nova explosion occurs its visibility will increase significantly to a value of +2, comparable to the brightness of the North Star.
It will be at that precise moment when we will be able to contemplate this new “star” with the naked eye for several days, without the help of any optical device, before it fades again and disappears, possibly for another 80 years.
We will witness a unique astronomical event: the thermonuclear explosion of a white dwarf. For those who do not know what is happening up there, an ephemeral star will have been born.
