A star can blink in space. It is part of a pair. One star pulls gas from the other. This gas makes hot spots. The spots shine bright. We see them blink like a light. Do you like to look at stars?
Some stars blink in space. They are part of a pair. One star pulls gas from its partner. This gas falls onto a small, heavy star. The heavy star has a strong pull. It pulls the gas to its top and bottom. This makes very hot spots. These spots are much brighter than our Sun. The spots shine bright light. The star spins around. This makes the light blink. We see it like a flashing lamp. It is a busy part of space.
Some stars blink in space. These are called X-ray pulsars. They are part of a pair of stars. One star is a neutron star. This star has a very strong magnetic field. It is a trillion times stronger than Earth's field.
A neutron star pulls gas from its partner star. This gas falls toward the neutron star. The magnetic field pulls the gas to the poles. This makes hot spots on the surface. These spots are very bright. They can be ten thousand times brighter than the Sun. The gas hits the surface very fast. This creates heat of millions of degrees. The heat lets out X-rays.
As the star spins, the spots move. They move in and out of our view. This makes the X-rays look like pulses. Some pulsars spin faster and faster. Others spin slower. This happens because the gas adds or takes away spin. The first one was found in 1971. It was named Centaurus X-3.
X-ray pulsars are amazing objects found in deep space. They belong to a group called accretion-powered pulsars. These objects send out X-rays in regular pulses. The time between pulses can change a lot. Some pulses happen every fraction of a second. Others take several minutes to repeat. They are part of a binary star system. This means two stars orbit each other. One star is a tiny, dense neutron star. The other is a stellar companion.
These pulsars work through a special way of moving gas. The neutron star has a huge magnetic field. It is about 108 tesla. This is a trillion times stronger than Earth's magnetic field. The neutron star pulls gas from its partner star. This gas follows the magnetic field lines. The gas travels to the magnetic poles. It creates hot spots on the surface. These spots are only one square kilometer in area. They can be ten thousand times brighter than the Sun.
Scientists first found these objects using special tools. They use X-ray telescopes on satellites in low Earth orbit. In the early years, they used balloons or rockets. The very first X-ray pulsar was Centaurus X-3. It was discovered in 1971. This discovery was made by the Uhuru X-ray satellite. Since then, we have found many more. Some are found in large, elliptical orbits. Others are part of a Be star system.
There are different ways the gas reaches the star. Some companion stars are huge OB supergiants. These stars have a radiation-driven wind. The neutron star catches gas from this wind. A system called Vela X-1 does this. In other systems, the stars are very close. This causes Roche lobe overflow. The gas forms a spinning accretion disc. This happens in the Cen X-3 system. Some stars, called Be stars, shed a disk of gas. The pulsar SXP 214 is an example.
How these stars spin is very interesting. They are different from radio pulsars. Radio pulsars usually spin down and slow down. X-ray pulsars can spin faster or slower. The gas from the partner star changes the spin. This is called transferring angular momentum. It can change the spin rate very quickly. Some pulsars are even called anomalous X-ray pulsars. These are actually magnetars. They are isolated and not in a pair.
X-ray pulsars, also called accretion-powered pulsars, are specialized astronomical objects. They are X-ray sources that show strict periodic variations in intensity. This means they emit flashes of X-rays at very regular intervals. These X-ray periods can be very short or quite long. Some pulses occur in just a fraction of a second. Other pulses may take several minutes to repeat. These objects are vital for understanding how matter behaves in extreme environments. They allow scientists to study the physics of dense stars and intense magnetic fields.
An X-ray pulsar is part of a binary star system. This system consists of a neutron star and a stellar companion. The neutron star has a massive magnetic field at its surface. This field strength is typically about 10^8 tesla. That is over a trillion times stronger than Earth's magnetic field. The neutron star pulls gas from its companion star through a process called accretion. This gas is channeled by the magnetic field toward the magnetic poles. This creates localized X-ray hot spots on the surface. These spots are similar to Earth's auroral zones but much hotter.
At these hot spots, the infalling gas moves incredibly fast. The gas can reach half the speed of light before impact. This movement releases a massive amount of gravitational potential energy. Because of this energy, the hot spots are extremely luminous. Each spot is estimated to be about one square kilometer in area. These spots can be ten thousand times or more as luminous as the Sun. The temperatures reach millions of degrees. This extreme heat causes the spots to emit mostly X-rays. As the neutron star rotates, these spots move in and out of view. This happens if the magnetic axis is tilted relative to the spin axis.
There are several ways that gas reaches the neutron star. In some systems, the companion is a massive OB supergiant star. These stars emit a radiation-driven stellar wind from their surfaces. The neutron star sits in this wind and captures the nearby gas. Vela X-1 is a known example of this type of system. In other systems, the stars orbit very closely to one another. This allows for a process called Roche lobe overflow. The neutron star's gravity pulls material from the companion's atmosphere. This material forms a gaseous accretion disc that spirals inward. The Cen X-3 system is a famous example of this process.
Another type involves a companion known as a Be star. These stars rotate very rapidly and shed a disk of gas around their equators. The neutron star usually has a large, elliptical orbit around these stars. When the neutron star passes through or near the circumstellar disk, it captures material. This makes the object temporarily become an X-ray pulsar. These are called transient X-ray pulsars because they are only observed intermittently. There can be months or even years between observable episodes. The SXP 214 system is an example of a Be-companion X-ray pulsar.
X-ray pulsars behave differently than radio pulsars regarding their spin. Radio pulsars are usually single objects that lose angular momentum. This causes them to slow down over time. X-ray pulsars are members of binary systems and accrete matter. This accreted matter transfers angular momentum to the neutron star. This transfer can cause the spin rate to increase or decrease. Some X-ray pulsars spin faster and faster or slower and slower. Others show erratic spin-up and spin-down behavior. These changes happen at rates hundreds of times faster than in radio pulsars.
Scientists have used various tools to observe these distant objects. Most observations are made using X-ray telescopes on satellites in low Earth orbit. In the early years of X-ray astronomy, researchers used balloons and sounding rockets. The first X-ray pulsar was discovered in 1971. It was named Centaurus X-3. This discovery was made using the Uhuru X-ray satellite.
It is important to distinguish X-ray pulsars from anomalous X-ray pulsars. Anomalous X-ray pulsars are actually magnetars. Magnetars are isolated, highly-magnetized neutron stars. They can be observed as relatively slow X-ray pulsars. Their periods are typically a few seconds long. Unlike standard X-ray pulsars, they are not part of a binary system. This distinction helps astronomers categorize the different ways neutron stars emit radiation.
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