The night sky sometimes holds spectacular surprises. Two new stars have appeared in less than two weeks, an extremely rare phenomenon.
These sudden bursts of light come from stellar explosions called classical novas. These events, where a white dwarf sucks matter from a companion star until it triggers an explosion, are usually observed once a year. Seeing two naked-eye novas simultaneously is exceptional.
Astronomers have spotted two 'new stars' shining simultaneously: V572 Velorum (left) and V462 Lupi (right). Credit: Eliot Herman
The first nova, V462 Lupi, was detected on June 12 in the constellation Lupus. The second, V572 Velorum, appeared on June 25 in the constellation Vela. According to
EarthSky.org, their brightness reached levels allowing naked-eye observation, an almost unprecedented occurrence.
Stephen O'Meara, an astronomer quoted by
Spaceweather.com, highlights the extreme rarity of this event. The last simultaneously visible novas date back to 1936, but they did not reach their peak brightness at the same time.
V572 Velorum shone more intensely, with an apparent magnitude of +4.8. V462 Lupi, though less bright, still reached a magnitude visible without instruments. These phenomena are more easily observable from the southern hemisphere, but V462 Lupi can be glimpsed from the northern hemisphere.
Locations of novas V462 Lupi and V572 Velorum in the constellations Lupus and Vela. Credit: IAU/Wikimedia, modified by Live Science
Novas differ from supernovas in their mechanism and impact. They do not destroy the star but release a significant amount of energy. Their study provides keys to understanding the evolution of binary star systems.
How does a nova form?
A nova occurs in a binary system where a white dwarf, the dense remnant of a Sun-like star, draws matter from a companion star. This matter, primarily hydrogen, accumulates on the white dwarf's surface.
Under the effect of intense gravity, pressure and temperature rise until they trigger an explosive nuclear fusion reaction. This explosion ejects some of the accumulated matter into space, producing a sudden increase in brightness.
Unlike supernovas, the white dwarf survives the explosion and can repeat the cycle. Some novas are recurrent, exploding at regular intervals when enough matter has accumulated again.
Studying novas helps astronomers better understand extreme physical processes in binary star systems and the distribution of chemical elements in the universe.
Why are some novas recurrent?
Recurrent novas, like T Coronae Borealis, occur in systems where the transfer of matter from the companion star to the white dwarf is continuous and rapid. This allows sufficient matter accumulation to trigger explosions at regular intervals.
The time between explosions depends on the matter transfer rate and the white dwarf's properties. In some cases, like RS Ophiuchi, explosions occur roughly every 20 years.
These systems are natural laboratories for studying matter accretion and thermonuclear explosions. They also play a role in enriching the interstellar medium with heavy elements.