In 2020, a change in the brightness of the star Betelgeuse has attracted the attention of astronomers and astronomy enthusiasts. This is because the star is in the final phase of its life and, in theory, could go supernova at any time. Many were excited at the prospect of observing a supernova with the naked eye, but in the end it was just a cloud of dust and gas that caused the effect.
The supernovae that can be observed with the naked eye are not very common, since most stars near the Sun have a similar age and type to its own. However, another type of stellar explosion may soon be seen here on Earth. This other type of explosion is called a nova and, although not as well known as the supernova, it is also an attention-grabbing event in the sky.
The University of Warwick issued a press release about the so-called nova event, which it is estimated to take place between June and September this year. The phenomenon can be observed with the naked eye and will be brighter than most stars in the sky. For a period of time it will be as if another bright star had formed in the sky and it is estimated that the next one will arrive only in 80 years.
White dwarfs
When a star with a low stellar mass reaches the end of its life, it can become a white dwarf. White dwarfs are examples of compact objects, such as black holes and neutron stars, but they are not as extreme as the others. They are small objects and it is estimated that they will be able to survive the current era of the universe.
White dwarfs can also cause a phenomenon called type Ia supernova, which is used to estimate the expansion rate of the universe. The Sun’s future is to become a white dwarf when it reaches the end of its life.
The first phase will consist of becoming a red giant for a few million years and then spending the rest of its life as a white dwarf. Most stars in a galaxy end up becoming white dwarfswhile only a percentage have enough mass to become black holes or neutron stars.
Binary stars
It is possible to find white dwarfs in binaries with other types of stars. This mainly occurs when one of the stars in an existing stellar binary reaches the end of its life. The result is that one of the stars will become a white dwarf if it has low mass, and the other will continue to orbit until it runs out of fuel to maintain balance.
A binary refers to a system of two stars gravitationally bound, so that they rotate around each other.
A type Ia supernova is an effect caused when mass transfer from the larger star to the white dwarf occurs in these binaries. If this mass exceeds a limit called Chandrasekhar limit, the white dwarf can explode, causing a type Ia supernova. Due to the mass limit of white dwarfs, almost all explosions have the same luminosity and are useful for measuring the distance and speed of the galaxy where the explosion occurred.
What is nine o’clock?
Another phenomenon that can occur in these binary systems is the nova. Nine o’clock occurs when the white dwarf attracts material from the other star in the binary system and creates a hydrogen envelope around the white dwarf. The greater the mass, the higher the temperature it can reach, which is necessary for hydrogen fusion.
When this limit temperature is reached, an explosion occurs which ends up expelling part of the gaseous surface of the star. During this process, we observe it as an explosion in the sky where the object becomes thousands of times brighter. One has the impression that a new star has formed, but little by little this brightness decreases until it returns to the initial value.
T Coronae Borealis
This is an effect that occurs in a binary system called T Coronae Borealis. It has been observed several times on Earth, as it is an event that occurs approximately every 80 years. Generally, a dip in the binary’s brightness occurs before the event occurs and this is what happens with the binary. Moreover, the last time was in 1946.
Another advantage of this particular binary is that it is located in a region of the sky where there is not a high density of stars. Therefore, it is possible to observe it even brighter than other stars. It is estimated to be even brighter than the Pole Star seen in the planet’s northern hemisphere.
How to observe the nova?
Since it is not possible to predict exactly when this explosion will occur, the odds point to the next few months. The binary is located in the constellation Corona Borealis, which is observed only in the Northern Hemisphere, so it can be seen from Europe. However, if you don’t want to miss the details of the event, the emissions provided by the European or American space agencies will constantly monitor the sky.
News reference:
Keep your eyes on the sky for a new star as “once in a lifetime” cosmic explosion looms
