Hot Helium Stars

Context:

Astronomers recently discovered out small, hot helium covered stars in binary system.

Key outcomes of discovery:

• Stars are cosmic engines which opens new doors to understand their influences on the universe, from the creation of heavy elements to the release of gravitational waves
• With a telescope capable of detecting ultraviolet light, observed around half a million stars in the Large and Small Magellanic Clouds
  • The Large Magellanic Cloud and the Small Magellanic Cloud – 2 dwarf galaxies which are companions to the Milky Way
• Some stars exhibited different speeds, hinting at the presence of companions (binary nature) affecting their free movement.
• Analysis of the optical spectra of 25 stars revealed their elemental composition led to the identification of different star classes. 
• Classified into 3 classes: 
  • Class 1 – Strong presence of helium and an absence of hydrogen (i.e helium-rich, hydrogen-depleted)
  • Class 2 and Class 3 – Some possessed hydrogen (i.e helium-rich, with hydrogen)

Why star doesn’t collapse onto itself?

• Due to Newton’s law of gravity –  All objects with mass attract each other
  • Sun’s outer and inner layers are attracted to each other, so the star should continuously fall inwards, and eventually simply collapse
• Fusion prevents the Sun from shrinking
  • Stars fuse light elements in their cores, like hydrogen, creating heavier nuclei and releasing immense heat. This energy counters gravity, sustaining stellar equilibrium by imparting random motion or pressure to particles.

Binary System of Stars:

• Refers to a pair of stars that orbits around a common centre of mass which are gravitationally bound to each other
• Perhaps up to 85% of stars are in binary systems with some in triple or even higher-multiple systems

Types of binary system:

• Visual Binaries –  
  • It consists of 2 stars that can be directly resolved and separated using a telescope
  • Easiest to identify
• Spectroscopic binaries –
  • Stars are too close together to be resolved visually even with powerful telescopes
  • Presence of stars can be detected by observing periodic shifts in their spectral lines
• Eclipsing Binaries –
  • Stars are aligned in a way that 1 star periodically passes in front of the other from our perspective
  • It creates a temporary dip in the brightness of the combined system, allowing astronomers to confirm the presence of the unseen companion and study its properties.
• Astrometric Binaries –
  • Stars are detected indirectly by measuring the wobbling motion of a single star
    Wobbling motion is due to the gravitational pull of the unseen companion star

Confirmation of Binary Systems:

• Occurs when a star exhausts its fuel, gravity takes over, leading to a supernova explosion that strips its outer layers
• Some supernova lack hydrogen, suggesting pre-explosion stripping of the outer layer
  • It happens in binary systems, where one star’s gravity removes the outer hydrogen layer from its companion, leaving behind a helium-rich star. 

Source: The Hindu

---

Previous Year Question

The terms ‘Event Horizon’, ‘Singularity’, ‘String Theory’ and ‘Standard Model’ are sometimes seen in the news in the context of

[UPSC Civil Services Exam – 2017 Prelims]

(a) Observation and understanding of the Universe
(b) Study of the solar and the lunar eclipses
(c) Placing satellites in the orbit of the Earth
(d) Origin and evolution of living organisms on the Earth

Answer: (a)

---