TAG: GS 3: SCIENCE AND TECHNOLOGY
THE CONTEXT: Astronomers have recently achieved a breakthrough in their quest to locate a unique class of stars – hot, helium-covered orbs that had eluded discovery for over a decade.
EXPLANATION:
- Led by Assistant Professor of the University of Toronto, a dedicated research team successfully confirmed a crucial prediction related to the evolution of binary stars.
Illustration of a kilonova explosion following the merger of two neutron stars
Theoretical Background: Gravity, Fusion, and Equilibrium
- To appreciate this discovery, one must understand the delicate interplay between gravity and nuclear fusion within stars.
- Despite Newton’s law of gravity suggesting the Sun should collapse onto itself, nuclear fusion in its core counteracts gravitational pull, maintaining the Sun’s equilibrium.
- Newton’s Law of Universal Gravitation states that every particle attracts every other particle in the universe with force directly proportional to the product of the masses and inversely proportional to the square of the distance between them.
- This equilibrium, known as the main sequence, is crucial for the stability of stars over billions of years.
- The study further delves into the phenomenon of binary star systems, where the gravitational influence of one star can strip away the hydrogen layer of its companion, leaving a hot helium star with strong surface gravity.
- Despite expectations of numerous such stars in the universe, only one binary system in the mass range of eight to 25 solar masses had been identified before this discovery.
Research Approach: Seven Years of Systematic Exploration
- The research team, committed to validating existing astrophysical theories, spent seven years cataloging thousands of stars, employing a meticulous working hypothesis.
- Their focus was on binary systems that initially comprised two main sequence stars, with one eventually becoming a helium star due to the stripping mechanism.
Ultraviolet Light Detection and speed analysis:
- Helium stars emit more ultraviolet radiation than main sequence stars.
- The researchers strategically used a telescope capable of detecting ultraviolet light to catalog around half a million stars in the Large and Small Magellanic Clouds.
- Bright outliers in the data were identified as potential helium stars.
- Studying the speeds of the identified stars revealed variations, indicating potential binary systems.
- This meticulous process led to a shortlist of 25 stars, which became the focus of the final test involving optical spectra analysis.
Spectral Analysis: Confirming Hydrogen-Stripped Helium Stars
- Optical spectra analysis, akin to deciphering a star’s fingerprint, revealed two distinct classes – Class 1 stars with a strong presence of helium and an absence of hydrogen, and Class 2 and Class 3 stars with varying hydrogen content.
- The team concluded that Class 1 stars are helium-rich and hydrogen-depleted, with companions being low-mass main sequence stars or compact objects such as neutron stars or black holes.
Computer Modeling: Unveiling the Characteristics of Class 1 Stars
- To further understand Class 1 stars, the researchers employed computer modeling.
- The surface temperature of these stars was estimated to be approximately 20 times that of the Sun, with a surface gravity around 1,000 times that of Earth.
- These findings painted a vivid picture of hot, strongly gravitating, helium-rich stars in binary systems.
- The research team predicts that Class 1 stars, once reaching the end of their lifecycle, will culminate in hydrogen-poor supernovae, leaving behind ultra-dense neutron stars.
- Furthermore, these neutron stars may eventually collide in powerful kilonova explosions, emitting gravitational waves.
Helium star:
- A helium star is a class O or B star (blue), which has extraordinarily strong helium lines and weaker than normal hydrogen lines, indicating strong stellar winds and a mass loss of the outer envelope.
- Extreme helium stars (EHe) entirely lack hydrogen in their spectra.
- Pure helium stars lie on or near a helium main sequence, analogous to the main sequence formed by the more common hydrogen stars.
Nuclear fusion:
- Nuclear fusion is defined as the combining of several small nuclei into one large nucleus with the subsequent release of huge amounts of energy.
- It is the opposite reaction of fission, where heavy isotopes are split apart.
- Nuclear fusion reaction involves combining two atomic nuclei to form a single heavier one, releasing an enormous amount of energy.
- Such reactions do not occur at room temperature and large amounts of energy are required to create conditions conducive to generating fusion-powered energy.
- It is the same fundamental reaction that powers the sun and other stars.
Conclusion: Bridging the Gap in Astrophysical Knowledge
- The discovery of hydrogen-stripped helium stars fills a significant gap in our understanding of stellar evolution. By confirming theoretical predictions, this research not only expands our knowledge of the cosmos but also opens avenues for exploring the diverse influences of stars on the universe, from the creation of heavy elements to the generation of gravitational waves.