A new star has exploded in the constellation Scorpio. This happened on June 6, but the news did not cause a significant resonance – this star is rather weak, not visible to the eye – at best through strong binoculars or a small telescope. And here, as well as possible, the proverb fits the case: “The new is the well-forgotten old” – this star was known to astronomers.
However, this case is remarkable.
Let’s take a look at what happened.
U Scorpii – as this star is designated in the catalogs of variable stars – has already flared up several times. This is not quite a “New Star” in the usual astronomical classification. Such stars are called “new-like” or “repeated novae”.
How are such stars different from the “Classic New”?
First of all, the frequency of regular outbreaks. Classical Nova flares up once every several thousand years, and astronomers practically did not observe repeated outbreaks of new ones, because astronomy itself is several thousand years old, and serious astronomy, which is an exact science supported by a strict mathematical apparatus, is only three hundred years old.
But scientific rigor is the whole point – studies of most new stars reveal some most likely period of accumulation of the resource of a star that flares up, becoming a dozen magnitudes brighter – about ten thousand times. It is clear that a lone star, which has already managed to burn all its resources, has nowhere to get new fuel for an outbreak. But if there is another quite wealthy star nearby, then a certain amount of hydrogen and helium from the neighboring star can be squeezed out.
Close binary stars flare up with new ones. One of them is a white dwarf who has already squandered all his fortune, but is not averse to squandering his neighbor’s. Another star – most often a giant or sub-giant – it still has something, it is very close, it is loose and willingly shares with a white dwarf – the gravity of the dwarf pulls the outer layers of a large and plump star in its direction, this substance twists into an accretion disk , turning the white dwarf into the likeness of the planet Saturn. As matter accumulates in the accretion disk, thermonuclear reactions resume in the zone of contact between the disk and the surface of the dwarf – this is a flash. The matter quickly burns out, and a new stage of pulling the matter from the sub-giant to the dwarf begins, which lasts those same thousands of years.
But in some cases, stellar vampirism proceeds more actively, and the substance necessary for an outbreak accumulates not over thousands of years, but tens. This is just the case of U Scorpio.
What allows matter to accumulate so quickly in the dwarf’s accretion disk?
Firstly, the dwarf must be massive – close to the limit of the possible mass of a dwarf, overstepping which we would no longer have a dwarf, but a neutron star – a denser and more massive stellar cinder.
Secondly, the proximity of the donor star.
And this is a portrait of the star system under discussion: the dwarf here is close in mass to the limit, and the donor star is very close – allegorically speaking, these stars almost touch each other, making a revolution around the common center of mass in a little over a day – this is a record-breaking fast orbital rotation among stars novice class. In addition, the stars in this dance outshine each other, which makes the U Scorpio system also an eclipsing variable star with a very noticeable amplitude of brightness change – about 2 magnitudes.
By the way, it will be said that science now knows only 10 new-like stars, among which is the rather well-known star T of the Northern crown, but it has a characteristic period between outbursts of about 80 years, and U Scorpio has about 10.
Every ten years U Scorpio gives a flash. But these outbreaks are very fleeting. Sometimes astronomers simply do not have time to notice a sudden increase in the brightness of a star and an equally rapid – in just a couple of days – fading, because the Sun is in the constellation Scorpio once a year – in November and December – a couple of months (at least) U Scorpio is inaccessible to observations. Even orbiting space telescopes are powerless here.
But still, since 1863, when the outburst of this star was first recorded, astronomers have been able to observe or identify 10 outbursts retroactively (from photographs). The 2010 flare was discovered by Florida amateur astronomer Barbara Harris — amateurs can also make a tangible contribution to the study of such unusual stars.
The outburst of 2022 was predicted with a fairly high degree of accuracy, and the star flared up as expected. The only pity is that its brightness – even at the moment of maximum brightness – did not reach the required for observing the star with the naked eye. And now – after a few days, the star has greatly weakened and can hardly be observed in amateur optics.
Now the brightness of the star U Scorpio is about the 12th magnitude – a little brighter than Pluto.
It can be guessed that over time the mass of the dwarf, which pulls the matter of a nearby satellite star towards itself, is constantly growing. And in the future, the dwarf will no longer be able to remain a dwarf – it will inevitably turn into a neutron star. And then, instead of the usual flash of a new-like star, we will see a supernova flash – this will be a more significant increase in brightness – not by 10,000 times, but by several million. And then U Scorpio will be visible to the naked human eye – if humans survive on Earth by that time, because this will not happen in our lifetime.
But the outbreak of a supernova in this case does not pose a danger, because U Scorpio is very far from us – 45 thousand light years in the direction of the star Antares – this is on the other side of the center of our Milky Way Galaxy.
As I have already noted, for amateur observations, the star U Scorpii is a complex object. But I’ll still leave the map where the new star is marked.