Astronomers found the small and hot helium stars they were looking for
- February 22, 2024
- Posted by: OptimizeIAS Team
- Category: DPN Topics
Astronomers found the small and hot helium stars they were looking for
Subject: Science and tech
Section: Space tech
Research details:
Led by assistant professor Maria Drout of the University of Toronto, the research team found these stars after spending seven years of hard work.
Outcome of Research :(Looking for):
A unique class of stars (are cosmic engines) hot and relatively small orbs covered in helium.
Importance of Research:
To understanding Stars’s diverse influences on the universe, from the creation of heavy elements to the release of gravitational waves.
Why Sun doesn’t collapse onto itself?
- Newton’s law of gravity says all objects with mass attract each other.
- Applying this – the Sun’s outer and inner layers should be attracted to each other, the Sun should continuously fall inwards and eventually simply collapse.
Yet the Sun rises every day, as it did yesterday and will tomorrow.
Reason: Nuclear fusion prevents the Sun from shrinking.
Nuclear Fusion: In the heart of the star, chemical reactions merge the nuclei of two light elements — such as hydrogen or helium — to form a heavier nucleus, such as of silicon. In the process releases an enormous amount of heat.
- This energy endows all particles in the star with random motion, or pressure, which then fights against the pull of gravity and maintains the star in a state of equilibrium.
Conclusion:
The fusion energy pushes the star out while gravity pulls it in, and they hold the balance for billions of years. Such stars are said to be in the main sequence.
Main sequence: On plotting stars’ colours against their brightness, many stars occupied a prominent band in the middle of the graph, referred as ‘main sequence’.
Other possibilities and associated features:
Supernova:
- When a star (heavy enough) no longer fuses material and gravity overtakes, then heavy enough star blows up in an explosion, called a supernova.
- By making scientific studies of light from supernovae it is observed that light contain signatures of elements that it passed.
- Also, some supernovae have no hydrogen. And yet it is well understood that hydrogen (lightest element ) makes up outer layer of main-sequence stars .
Explanation of this:
- The outer layers of some stars are stripped away before the supernova explosion.
- Reason behind this(No hydrogen/outer layer stripped off):
- If the star is part of a binary system — i.e. as one of two stars that are orbiting each other. (Most stars heavier than the Sun are in such binaries.)
- Then the gravitational attraction of one star can peel away the hydrogen layer off the other, leaving an exposed surface of helium. This would leave a small, hot helium star with strong surface gravity.
Stars part of Binary system:
- Most stars with more than eight solar masses are expected to be part of binary systems, so we should reasonably expect numerous binary-stripped helium stars in the universe.
- Present availability of Binary system:
- Till date, astronomers have found exactly one binary system in the mass range of eight to 25 solar masses (prior to stripping), and have been looking for the others.
- Recent findings- Main companion star and bright outliers analysis:
- Drout & co. have now reported a population of these stars.
- Many binary systems start out with two main sequence stars.One of them rips the hydrogen layer off the other-resulting in one helium star and one main sequence companion.
- to team, the companion would outshine the stripped star in the frequencies of light (both human eyes as well as optical telescopes are sensitive to it )
- Different frequencies roughly correspond to different colours of light.
- The hotter an object is, the more energy it has, the higher the frequency of emitted light, and the bluer it glows.
- Helium stars are expected to be so hot that they emit more of their energy as ultraviolet radiation, which lies beyond the visible range.
- So, the research catalogued around half a million stars in two nearby galaxies — the Large and the Small Magellanic Clouds — using data from a telescope that could ‘see’ ultraviolet light.
Most of the stars were main sequence stars, but also some bright outliers.
Speed analysis findings:
- If a star were isolated, it would be seen moving either towards or away from the earth at a constant rate.
- But some of the outliers had different speeds over time – hinting at the presence of a companion that restricted their free movement.
When the researchers examined the spectra of the 25 stars- they found–
Class 1: Several with a strong presence of helium and an absence of hydrogen.
Class 2 and Class 3: Some possessed hydrogen as well.
Based on this, the team made two conclusions:
(1) Class 1 stars have no hydrogen and are rich in helium
(2) their companions are either low-mass not-as-bright main sequence stars or compact objects (neutron stars or blackholes) that don’t emit ultraviolet light strongly.
On various researches it is concluded:
The surface temperature of Class 1 stars to be roughly 20-timesthat of the Sun and the surface gravity about 1,000-times that of the earth.
Hence, Class 1 are hot, strongly gravitating, helium-rich, and hydrogen-depleted stars and part of binary systems.
Final outcome:
The team discovered the long-awaited intermediate-mass hydrogen-stripped helium stars in binaries after seven years.
And, These stars will end their lives as hydrogen-poor supernovae that leave behind ultra-dense balls called neutron stars. And these neutron stars may ultimately smash into each other in powerful kilonova explosions, releasing gravitational waves.