23.4 Pulsars and the Discovery of Neutron Stars
3 min read•june 12, 2024
Neutron stars, discovered in 1967, are incredibly dense cosmic objects that emit regular radio pulses. These fascinating remnants of massive stars pack up to 3 solar masses into a sphere just 20 km wide, spinning rapidly with intense magnetic fields.
, a type of , were initially mistaken for alien signals due to their precise timing. Their discovery revolutionized our understanding of and provided crucial evidence linking these compact objects to explosions.
Discovery and Characteristics of Neutron Stars and Pulsars
Steps in neutron star discovery
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THE GRANDMA'S LOGBOOK ---: JOCELYN BELL BURNELL: THE FIRST RADIO PULSARS View original
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- In 1967, and detected regular radio pulses from a distant cosmic source
- Pulses had a precise period of 1.33 seconds
- Initially thought to be signals from an extraterrestrial civilization due to their regularity
- Source named (Little Green Men 1) before being identified as a rapidly rotating neutron star
- Neutron stars emit electromagnetic radiation, primarily radio waves, which allows for their detection despite their extreme distances
- Closest known neutron star is about 400 light-years from Earth ()
- Radio telescopes are used to detect the faint, regular pulses emitted by neutron stars
- Regularity of pulses distinguishes them from other radio sources (galaxies, quasars)
Characteristics for pulsar detection
- Neutron stars have extremely high densities, with 1.4 to 3 solar masses compressed into a sphere about 20 km in diameter
- High density results from the collapse of a massive star's core during a supernova explosion
- Powerful magnetic fields, typically around gauss, about a trillion times stronger than Earth's magnetic field
- Strong magnetic fields created during core collapse and conservation of magnetic flux
- Rapid rotation, with periods ranging from milliseconds to several seconds
- Rapid rotation caused by conservation of angular momentum during core collapse
- Combination of strong magnetic fields and rapid rotation leads to emission of focused beams of electromagnetic radiation from the neutron star's magnetic poles
- Beams sweeping across Earth as the neutron star rotates are observed as pulses, hence the term ""
- Regular emissions enable precise timing measurements, making them useful for studying astronomical phenomena and testing theories of gravity
Evidence linking pulsars to supernovae
- , a supernova remnant from 1054 CE, contains the at its center
- Provides direct evidence linking neutron stars to supernova explosions
- Other supernova remnants (, ) have been found to contain pulsars
- Pulsars believed to be compact remnants of massive stars that exploded as supernovae
- Rapid rotation and strong magnetic fields of pulsars are consistent with properties expected from a collapsed stellar core following a supernova
- Theoretical models of core-collapse supernovae predict the formation of neutron stars
- Models supported by observed association between pulsars and supernova remnants
- Distribution of pulsars in the Milky Way is consistent with their formation in supernova events
- Pulsars more commonly found in the galactic plane, where most massive stars reside and end their lives as supernovae
Stellar Evolution and Compact Objects
- describes the life cycle of stars, from birth to death
- Massive stars (>8 solar masses) end their lives in supernova explosions, potentially forming neutron stars
- Less massive stars may become white dwarfs, supported by electron degeneracy pressure
- The (~1.4 solar masses) is the maximum mass for a stable
- Stars exceeding this limit will collapse further, potentially becoming neutron stars
Key Terms to Review (36)
Antony Hewish: Antony Hewish was a British radio astronomer who made significant contributions to the discovery and understanding of pulsars, which are rapidly rotating neutron stars that emit beams of electromagnetic radiation. His work was crucial in the identification and characterization of these celestial objects, leading to a greater understanding of the nature of neutron stars and their role in the universe.
Bell: Bell refers to Jocelyn Bell Burnell, the astrophysicist who discovered the first radio pulsars in 1967. Her discovery provided crucial evidence for the existence of neutron stars and revolutionized our understanding of stellar evolution.
Binary Pulsar: A binary pulsar is a system consisting of two neutron stars, one of which is a rapidly rotating and highly magnetized neutron star known as a pulsar, orbiting a common center of mass. This unique system provides insights into the properties of neutron stars and the nature of gravity.
Black widow pulsar: A black widow pulsar is a type of millisecond pulsar that forms in a binary star system, where the pulsar's intense radiation and stellar wind gradually strip away and consume its companion star. This evolutionary process can lead to the eventual destruction of the companion star.
Cassiopeia A: Cassiopeia A is the remnant of a supernova explosion that occurred approximately 300 years ago in the constellation Cassiopeia. It is one of the most studied and well-known supernova remnants in the Milky Way galaxy, providing valuable insights into the processes that occur during and after a star's violent death.
Chandrasekhar limit: The Chandrasekhar limit is the maximum mass (approximately 1.4 times the mass of the Sun) that a white dwarf star can have before it collapses under its own gravity. Beyond this limit, the white dwarf will undergo further gravitational collapse to form a neutron star or black hole.
Chandrasekhar Limit: The Chandrasekhar limit is the maximum mass above which a star can no longer support itself against gravitational collapse after exhausting its nuclear fuel. It is a critical threshold that determines the fate of a star's evolution and the type of stellar remnant it will leave behind.
Crab Nebula: The Crab Nebula is a supernova remnant, the expanding debris field from the explosion of a massive star. It is located in the constellation of Taurus and is one of the most studied and well-known objects in the night sky, providing insights into the aftermath of a star's death and the formation of neutron stars.
Crab Pulsar: The Crab Pulsar is a rapidly rotating neutron star located at the center of the Crab Nebula, a supernova remnant. It is one of the most studied and well-known pulsars, providing crucial insights into the nature of neutron stars and the processes that govern stellar evolution.
Degenerate Matter: Degenerate matter is an extreme state of matter that occurs in the cores of collapsed stars, such as white dwarfs and neutron stars. It is characterized by extremely high densities and pressure, where the electrons are forced to occupy higher-energy quantum states, resulting in unique physical properties.
Earth’s magnetosphere: Earth's magnetosphere is the region of space surrounding Earth that is controlled by its magnetic field. It protects the planet from solar and cosmic particle radiation and influences atmospheric phenomena.
Five-hundred-meter Aperture Spherical radio Telescope (FAST): The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the world's largest filled-aperture radio telescope, located in Guizhou, China. It is used for a variety of astronomical observations including pulsar discovery and interstellar communication research.
Gravitational Collapse: Gravitational collapse is the process by which a massive object, such as a star or cloud of gas and dust, contracts under its own gravitational attraction. This contraction can lead to the formation of various celestial bodies and the release of tremendous amounts of energy.
Hewish: Jocelyn Bell Burnell and Antony Hewish are credited with the discovery of pulsars in 1967. Hewish was awarded the Nobel Prize in Physics in 1974 for this groundbreaking work.
Jocelyn Bell Burnell: Jocelyn Bell Burnell is a pioneering astrophysicist who made a groundbreaking discovery that revolutionized our understanding of the universe. Her work was instrumental in the detection and study of pulsars, which are rapidly rotating neutron stars, as well as the development of radio telescopes, the primary tools used to observe these celestial phenomena.
Kepler’s Supernova: Kepler’s Supernova is a Type Ia supernova that was observed in 1604 within the Milky Way galaxy. Named after astronomer Johannes Kepler, it is one of the few supernovae visible to the naked eye in recorded history.
LGM-1: LGM-1, short for Little Green Men 1, was the name given to the first pulsar discovered in 1967. Pulsars are rapidly rotating neutron stars that emit beams of electromagnetic radiation, and the discovery of LGM-1 was a pivotal moment in the understanding of these celestial objects and the nature of neutron stars.
Lighthouse Effect: The lighthouse effect refers to the periodic flashes of light emitted by pulsars, which are rapidly rotating neutron stars. These pulsars act like cosmic lighthouses, sweeping a beam of electromagnetic radiation across the sky as they spin, allowing us to detect and study these unique celestial objects.
Magnetosphere: The magnetosphere is the region around a planet or other celestial body where the body's magnetic field dominates and interacts with the solar wind. It acts as a protective shield, deflecting charged particles and cosmic radiation, and plays a crucial role in the planet's overall structure and environment.
Millisecond Pulsar: A millisecond pulsar is a type of rapidly rotating neutron star that emits radio waves in extremely short, regular pulses. These pulsars are characterized by their incredibly fast rotation periods, often less than 20 milliseconds, making them the fastest spinning stars known to exist in the universe.
Neutron Star: A neutron star is an extremely dense, collapsed stellar remnant that forms when a massive star runs out of fuel and undergoes a supernova explosion, leaving behind a core so dense that the electrons are forced to combine with protons, creating a star composed almost entirely of neutrons. These incredibly dense objects have immense gravitational fields and are some of the most extreme objects in the universe.
Period-Luminosity Relation: The period-luminosity relation is a fundamental correlation observed between the pulsation period and the intrinsic luminosity (absolute brightness) of certain types of variable stars, particularly Cepheid variables and RR Lyrae variables. This relationship provides a powerful tool for determining the distances to these stars and, by extension, the structure and evolution of the universe.
PSR J0108-1431: PSR J0108-1431 is a pulsar, a rapidly rotating, highly magnetized neutron star that emits beams of electromagnetic radiation. It is one of the closest known pulsars to Earth and has been extensively studied to provide insights into the nature and evolution of neutron stars.
Pulsar: A pulsar is a highly magnetized, rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. These beams are observable when they sweep past Earth, appearing as regular pulses of radiation.
Pulsar: A pulsar is a highly magnetized, rapidly rotating neutron star that emits beams of electromagnetic radiation from its poles. These beams of radiation are observed as regular pulses of light, radio waves, or other forms of electromagnetic energy as the pulsar rotates, making pulsars some of the most fascinating and unique objects in the universe.
Pulsars: Pulsars are highly magnetized, rotating neutron stars that emit beams of electromagnetic radiation out of their magnetic poles. These beams are detectable when they sweep past Earth, creating a pulsed appearance.
Pulse Timing Analysis: Pulse timing analysis is a technique used in the study of pulsars, rapidly rotating neutron stars that emit beams of electromagnetic radiation. This method involves precisely measuring the arrival times of the periodic pulses emitted by pulsars, which provides insights into their properties and the nature of neutron stars.
Radio Spectroscopy: Radio spectroscopy is a powerful technique in astronomy that analyzes the radio waves emitted by celestial objects to gain insights into their physical properties and composition. It is a crucial tool in the study of pulsars and the discovery of neutron stars.
Radio Telescope: A radio telescope is a specialized astronomical instrument designed to detect and analyze radio waves emitted by celestial objects. These telescopes are used to study a wide range of phenomena in the universe, from the structure of galaxies to the formation of stars and planets.
SN 1054: SN 1054 is a supernova that was first observed in the year 1054 AD by astronomers in several different cultures. Its remnants form the Crab Nebula, which is one of the most studied astronomical objects today.
Stellar evolution: Stellar evolution is the process by which a star changes over the course of time. It encompasses the formation, life cycle, and eventual fate of stars.
Stellar Evolution: Stellar evolution is the process by which a star changes over the course of its lifetime, from birth to death. This term encompasses the various stages and transformations a star undergoes, driven by the complex interplay of gravitational, thermal, and nuclear forces within the star. Understanding stellar evolution is crucial in astronomy, as it provides insights into the life cycle of stars and their impact on the broader cosmic landscape.
Supernova: A supernova is a powerful and luminous stellar explosion that occurs at the end of a massive star's life cycle. It is one of the most energetic and dramatic events in the universe, releasing an immense amount of energy and ejecting vast amounts of material into space.
Vela: Vela is the name of a pulsar, a rapidly rotating and highly magnetized neutron star that emits beams of electromagnetic radiation. It is a key object in the context of understanding pulsars and the discovery of neutron stars.
White dwarf: A white dwarf is the remnant of a low to medium mass star that has exhausted its nuclear fuel and shed its outer layers. It is incredibly dense, with a mass comparable to the Sun but a volume similar to Earth.
White Dwarf: A white dwarf is the dense, compact remnant of a low-mass star that has exhausted its nuclear fuel and shed its outer layers, leaving behind a core composed primarily of degenerate matter. This stellar endpoint is a crucial component in understanding the evolution of stars and the structure of the universe.