Low-mass x-ray binary

Definition

A low-mass x-ray binary is a type of binary star system where one star is a compact object, like a neutron star or black hole, and the other is a low-mass star, typically less than 2 solar masses. In these systems, the low-mass star transfers material to the compact object, which leads to the formation of an accretion disk and the emission of X-rays due to the gravitational energy being converted into heat and light as the material spirals inwards.

5 Must Know Facts For Your Next Test

1. Low-mass x-ray binaries usually involve a companion star that fills its Roche lobe, allowing material to flow towards the compact object.
2. The X-ray emissions from low-mass x-ray binaries can be several orders of magnitude brighter than other types of stars, making them key targets for X-ray astronomy.
3. These systems often exhibit variability in their X-ray output due to changes in the rate of material being transferred from the companion star.
4. The mass transfer in low-mass x-ray binaries can lead to significant changes in the companion star's structure, eventually stripping it of its outer layers.
5. Some low-mass x-ray binaries are believed to evolve into type I X-ray bursts, which are sudden increases in brightness caused by thermonuclear explosions on the surface of the neutron star.

Review Questions

• How does the mass transfer process occur in low-mass x-ray binaries and what are its implications for both stars involved?
  • In low-mass x-ray binaries, the companion star transfers material to the compact object when it overflows its Roche lobe. This process creates an accretion disk around the compact object, where gravitational forces heat the infalling material to extreme temperatures, leading to X-ray emissions. The implications for both stars include potential structural changes in the low-mass companion as it loses mass and an increase in energy output from the compact object due to accretion.
• Discuss the significance of X-ray emissions in low-mass x-ray binaries and how they contribute to our understanding of these systems.
  • X-ray emissions are crucial for studying low-mass x-ray binaries because they provide insight into the accretion processes occurring in these systems. The intense X-rays emitted allow astronomers to measure the mass transfer rate and study the dynamics within the accretion disk. Additionally, variations in X-ray brightness can indicate changes in mass transfer rates or even help identify specific phases of binary evolution, thus enhancing our understanding of stellar evolution and compact objects.
• Evaluate how low-mass x-ray binaries serve as laboratories for testing theories about gravitational physics and extreme states of matter.
  • Low-mass x-ray binaries are unique environments that allow scientists to test theories about gravitational physics due to the extreme conditions present near compact objects like neutron stars or black holes. The high gravitational fields and rapid rotation rates enable researchers to study relativistic effects and test predictions of general relativity. Additionally, observing how matter behaves under such extreme pressures helps refine models of state changes in matter, particularly during accretion events, thereby advancing our understanding of physics under extreme conditions.

Related terms

Accretion Disk:

A structure formed by diffused material in orbital motion around a central body, where the gravitational forces lead to the heating and acceleration of matter.

Neutron Star: An extremely dense stellar remnant that remains after a supernova explosion, composed primarily of neutrons and typically having a mass between 1.4 and 3 solar masses.

X-ray Emission: The process by which X-rays are produced when high-energy electrons collide with atoms, often seen in astronomical phenomena such as black holes and neutron stars.