Question

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences. Which of these isolated neutron stars must have had a binary companion? (a) a pulsar inside a supernova remnant that pulses 30 times per second (b) an isolated pulsar that pulses 600 times per second (c) a neutron star that does not pulse at all

Short answer

The isolated pulsar that pulses 600 times per second likely had a binary companion.

Step-by-step solution

Understand the Characteristics

In this question, we need to determine which type of neutron star could have had a binary companion. We are given three characteristics of neutron stars: one that pulses 30 times per second (associated with being young and usually found in supernova remnants), one that pulses 600 times per second (known as a millisecond pulsar), and one that does not pulse at all.

Analyzing Pulsar Characteristics

A millisecond pulsar spins extremely rapidly (hundreds of times per second) and is often associated with having been in a binary system. Such a high rotation rate can be caused by angular momentum transfer from a companion during accretion processes, which can only happen in a binary system.

Applying Knowledge of Neutron Star Evolution

A pulsar inside a supernova remnant suggests a young pulsar that likely has not interacted significantly with another star, as it still retains its first burst of rotation from the supernova impact. A neutron star that does not pulse could be an old one that has slowed down, moving it away from the likely scenario of it being spun up by a binary companion.

Concluding the Most Likely Candidate

Based on the analysis, the isolated pulsar that pulses 600 times per second is most likely to have originated from a binary system. This is because its rapid rotation is characteristic of having been spun up by accretion from a companion.

Key concepts

Pulsars

Pulsars are fascinating celestial objects known for their lighthouse-like beams of radiation that sweep across space. These beams are emitted from a rotating neutron star, which is a remnant of a massive star that has undergone a supernova explosion. As the neutron star spins, its magnetic poles, which do not align with its axis of rotation, emit beams of radio waves.
When these beams are aligned with Earth, they are detectable as pulsating signals, hence the name "pulsar."

Key characteristics of pulsars include:

• Incredibly dense structure – a teaspoon of neutron star material weighs billions of tons!
• Rapid rotation rates – pulsars can rotate several hundred times per second.
• Strong magnetic fields – often trillions of times stronger than Earth's magnetic field.

Understanding pulsars helps astronomers to study the behavior of matter under extreme conditions, making these objects crucial in the field of astrophysics.

Binary Star Systems

A binary star system consists of two stars that orbit a common center of mass. These systems can significantly influence the evolution of their stellar components through interactions such as mass transfer or tidal forces.
Binary systems are especially important in the study of neutron stars, as they explain certain phenomena like millisecond pulsars.

Two stars in a binary system can be close or far apart:

• Close binary systems often see mass transfer, where material from one star accretes onto the compact object like a neutron star.
• Wide binary systems may not interact significantly over their lifetimes, leaving each star to evolve independently.

During mass transfer, the angular momentum from the accreting material can spin up a neutron star to become a millisecond pulsar. This process provides strong evidence of a previous binary companion, particularly in cases involving rapidly rotating pulsars.

Supernova Remnants

Supernova remnants are the incredible leftovers of massive stars that have ended their lives in colossal explosions. These remnants are composed of materials expelled during the supernova and often contain a neutron star or pulsar at their core.

Key features of supernova remnants include:

• Expanding shells of gas and dust that move through space at high velocities.
• Rich chemical compositions that can include elements such as hydrogen, oxygen, and iron.
• Some remnants may host pulsars, which are newly formed and often rapidly spinning.

Finding a pulsar within a supernova remnant typically suggests it is relatively young because it still retains the dramatic rotation thrust instigated by the supernova.
Supernova remnants provide valuable insights into the life cycles of stars, enriching our understanding of universe formation processes.

Millisecond Pulsars

Millisecond pulsars are among the most rapidly rotating objects in the universe, spinning hundreds of times per second. These pulsars have been spun up to such extraordinary speeds through the transfer of mass and angular momentum from a companion star in a binary system.
This makes them unique and different from the ordinary pulsars formed directly from supernovae.

Characteristics of millisecond pulsars include:

• Rotation periods of a few milliseconds.
• Incredibly stable rotational speeds, making them precise cosmic clocks.
• Usually found in binary systems, often associated with white dwarf companions.

The study of millisecond pulsars has provided astronomers with crucial data on phenomena like gravitational waves and the equation of state for neutron-star matter, thus enriching our overall comprehension of astrophysical processes.