Any night now, a “new star” or nova will appear in the night sky. Although it won’t set the sky on fire, it’s a special opportunity to witness a rare phenomenon that’s usually difficult to predict in advance.
The star in question is T Coronae Borealis (T CrB, pronounced “T Cor Bor”). It is located in the Northern Crown constellation, prominent in the Northern Hemisphere, but will also be visible in the northern sky from Australia and Aotearoa New Zealand over the next few months.
Most of the time T CREB, which is 3,000 light-years away, is too dim to be seen. But once every 80 years it explodes brightly.
Suddenly a new star appears, although it does not last long. After a few nights it fades rapidly and disappears into the darkness.
a burst of life
At the peak of their lives, stars are powered by nuclear fusion reactions deep inside their cores. Most commonly, hydrogen is converted into helium giving the star enough energy to remain stable and shining for billions of years.
But T CrB is well past its peak and is now a stellar remnant known as a white dwarf. Its internal nuclear fire has died down, allowing the force of gravity to dramatically compress the dead star.
A white dwarf is about the same size as Earth but is 300,000 times more massive, producing a powerful gravitational field. ESA/NASA.
T CrB also has a stellar companion – a red giant that has swelled as it entered old age. The white dwarf sucks up the swollen red giant’s gas, and this forms what is known as an accretion disk around the dead star.
Matter continues to accumulate on the star that has already been compressed to its limits, causing pressure and temperature to steadily increase. Conditions become so extreme, that they resemble those once found inside the star’s core. Its surface ignites in an uncontrolled thermonuclear reaction.
When this happens, the energy released makes T CrB 1,500 times brighter than normal. Here on Earth, it becomes briefly visible in the night sky. With this dramatic reset, the star expels the gas and the cycle can begin again.
How do we know when it’s due?
T CrB is the brightest of a rare class of recurring novae that repeat within a hundred years – a time scale that allows astronomers to detect their recurring nature.
Only ten recurring novae are currently known, although many more may be recurring – but on much longer timescales, which are less easy to detect.
The oldest known date for an eruption of T CrB is from the year 1217, based on observations recorded in medieval monastic chronicles. It is remarkable that astronomers can now predict its eruptions so accurately, provided that the nova follows its usual pattern.
The star’s two most recent explosions – in 1866 and 1946 – showed exactly the same features. About ten years before the explosion, T CrB’s brightness increased slightly (known as the peak phase) and then faded or declined slightly about a year after the explosion.
T CrB reached its peak in 2015 and a decline was observed before the explosion in March 2023, which alarmed astronomers. What causes these events is one of the few current mysteries surrounding T CrB.
How can I see this?
Start stargazing now! It’s a good idea to get into the habit of looking at Corona Borealis as it is now, so you can get the full effect of the “new” star.
Corona Borealis currently reaches its best observation position (known as a meridional transit) between 8:30 and 9 p.m. local time in Australia and Aotearoa. The further north you are located, the higher in the sky the constellation will appear.
The further north you are, the higher Corona Borealis will appear in the northern sky. The new star will be about as bright as Alpheus in Corona Borealis or nearby Rasalhague in Ophiuchus. Museum Victoria/Stellarium.
While south of Hobart, Corona Borealis remains low in the north. The bright star Arcturus serves as a good guide. Museum Victoria/Stellarium.
In Aotearoa, T CrB is best seen around 9pm throughout July. Additional constellations are shown for reference. Museum Victoria/Stellarium.
The nova is expected to be of reasonable brightness (magnitude 2.5): about as bright as Imai (Delta Crucis), the fourth brightest star in the Southern Cross. So if you know where to look, it should be easy to see it even from the city.
During July evenings, Southern Crux can be seen high in the southwest from Australia and Aotearoa. Museum Victoria/Stellarium.
we won’t have much time
Once it goes off the grid we won’t have much time. The maximum brightness will last only a few hours; within a week T CrB will fade and you’ll need a telescope to see it.
It will almost certainly be an amateur astronomer who will alert the professional community to the moment of T CrB’s explosion.
These dedicated and knowledgeable people regularly look up at the stars from their backyards, anticipating what might happen, and thus filling a vital gap in observing the night sky.
The American Association of Variable Star Observing (AAVSO) has a log of more than 270,000 submitted observations on T CrB alone. Amateur astronomers here and around the world are collaborating to continuously monitor for the first signs of an eruption of T CrB.
By September, Corona Borealis will move low in the northwestern sky and will be best seen between 7:30 and 8 p.m. local time. Museum Victoria/Stellarium.
The nova is expected to explode sometime before October as expected, as Corona Borealis will then be gone from our evening sky in the Southern Hemisphere.
,Author: Tanya Hill, Senior Curator (Astronomy), Museum Victoria and University of Melbourne, Honorary Fellow at the Museum Victoria Research Institute and Amanda Karakas, Associate Professor, School of Physics and Astronomy, Monash University,
,disclosure statement: Amanda Karakas receives funding from the Australian Research Council. Tanya Hill does not work for, consult, hold shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond her academic appointment)
This article is republished from The Conversation under a Creative Commons license. Read the original article.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
