Pulsar : The Flickering Giants
What is a PULSAR...
A pulsar is a highly magnetized rotating neutron star or white dwarf that emits a beam of electromagnetic radiation. This radiation can be observed only when the beam of emission is pointing toward Earth, and is responsible for the pulsed appearance of emission. Neutron stars are very dense, and have short, regular rotational periods.
From Earth, pulsars often look like flickering stars. On and off, on and off, they seem to blink with a regular rhythm. But the light from pulsars does not actually flicker or pulse, and these objects are not actually stars.
Pulsars radiate two steady, narrow beams of light in opposite directions. Although the light from the beam is steady, pulsars appear to flicker because they also spin. It's the same reason a lighthouse appears to blink when seen by a sailor on the ocean: As the pulsar rotates, the beam of light may sweep across the Earth, then swing out of view, then swing back around again. To an astronomer on the ground, the light goes in and out of view, giving the impression that the pulsar is blinking on and off. The reason a pulsar's light beam spins around like a lighthouse beam is that the pulsar's beam of light is typically not aligned with the pulsar's axis of rotation.
Pulsars spin because the stars from which they formed also rotate, and the collapse of the stellar material will naturally increase the pulsar's rotation speed. (Bringing mass closer to the center of a spinning object increases its rotation speed, which is why figure skaters can spin faster by pulling their arms in toward their torso.)
Pulsars are the size of small cities, so ramping them up to such high speeds is no small feat. In fact, millisecond pulsars require an additional source of energy to get going to such a high rotation rate.
Spinning in a Pulsar...
The slowest pulsars ever detected spin on the order of once per second, and these are typically called slow pulsars. The fastest known pulsars can spin hundreds of times per second, and are known as fast pulsars or millisecond pulsars (because their spin period is measured in milliseconds).Pulsars spin because the stars from which they formed also rotate, and the collapse of the stellar material will naturally increase the pulsar's rotation speed. (Bringing mass closer to the center of a spinning object increases its rotation speed, which is why figure skaters can spin faster by pulling their arms in toward their torso.)
Pulsars are the size of small cities, so ramping them up to such high speeds is no small feat. In fact, millisecond pulsars require an additional source of energy to get going to such a high rotation rate.
WHY do Pulsar radiate...
Pulsars can radiate light in multiple wavelengths, from radio waves all the way up to gamma-rays, the most energetic form of light in the universe.
according to Alice Harding, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who specializes in pulsars. What's more, scientists have found that different mechanisms are likely responsible for producing different wavelengths of light from the area above the pulsar's surface, Harding said. The lighthouse-like beams of light that scientists first spotted in the 1960s consist of radio waves. These beams of light are notable because they are extremely bright and narrow, and have properties similar to those of a laser beam. Laser light is "coherent," as opposed to non-coherent light radiated by, for example, a light bulb. In a beam of coherent light, the particles of light are essentially marching in step, creating a uniform, focused beam. When particles of light work together in this way, they can produce a beam of light that is exponentially brighter than a diffuse light source using the same amount of power.
What does seem clear to scientists is that pulsar emissions are powered by the pulsar's rotation and its magnetic field, according to Roger Romani, a professor of physics at Stanford University who studies pulsars and other compact objects. The fastest-spinning pulsars have weaker magnetic fields than slower spinning pulsars do, but the increase in rotation speed is still enough to cause those fast pulsars to radiate similarly bright beams to those of slower pulsars.
The light emitted by a pulsar carries information about these objects and what is happening inside them. That means pulsars give scientists information about the physics of neutron stars, which are the densest material in the universe (with the exception of whatever happens to matter inside a black hole). Under such incredible pressure, matter behaves in ways not seen before in any other environment in the universe. The strange state of matter inside neutron stars is what scientists call "nuclear pasta": Sometimes, the atoms arrange themselves in flat sheets, like lasagna, or spirals like fusilli, or small nuggets like gnocchi.
Some pulsars also prove extremely useful because of the precision of their pulses. There are many known pulsars that blink with such precise regularity; they are considered the most accurate natural clocks in the universe. As a result, scientists can watch for changes in a pulsar's blinking that could indicate something happening in the space nearby.
It was with this method that scientists began to identify the presence of alien planets orbiting these dense objects. In fact, the first planet outside Earth's solar system ever found was orbiting a pulsar.
Because pulsars are moving through space while also blinking a regular number of times per second, scientists can use many pulsars to calculate cosmic distances. The changing position of the pulsar means the light it emits takes more or less time to reach Earth. Thanks to the exquisite timing of the pulses, scientists have made some of the most accurate distance measurements of cosmic objects.
Pulsars have been used to test aspects of Albert Einstein's theory of general relativity, such as the universal force of gravity.
The regular timing of pulsars also may be disrupted by gravitational waves — the ripples in space-time predicted by Einstein and directly detected for the first time in February 2016. There are multiple experiments currently searching for gravitational waves via this pulsar method.
Using pulsars for these types of applications depends on how settled they are in their rotation (thus providing very regular blinks), Ransom said. All pulsars are slowing down gradually as they spin; but those used for precision measurements are slowing down at an incredibly slow rate, so scientists can still use them as stable time-keeping devices.
Pulsars can radiate light in multiple wavelengths, from radio waves all the way up to gamma-rays, the most energetic form of light in the universe.
according to Alice Harding, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who specializes in pulsars. What's more, scientists have found that different mechanisms are likely responsible for producing different wavelengths of light from the area above the pulsar's surface, Harding said. The lighthouse-like beams of light that scientists first spotted in the 1960s consist of radio waves. These beams of light are notable because they are extremely bright and narrow, and have properties similar to those of a laser beam. Laser light is "coherent," as opposed to non-coherent light radiated by, for example, a light bulb. In a beam of coherent light, the particles of light are essentially marching in step, creating a uniform, focused beam. When particles of light work together in this way, they can produce a beam of light that is exponentially brighter than a diffuse light source using the same amount of power.
What does seem clear to scientists is that pulsar emissions are powered by the pulsar's rotation and its magnetic field, according to Roger Romani, a professor of physics at Stanford University who studies pulsars and other compact objects. The fastest-spinning pulsars have weaker magnetic fields than slower spinning pulsars do, but the increase in rotation speed is still enough to cause those fast pulsars to radiate similarly bright beams to those of slower pulsars.
APPLICATION of Pulsars...
Pulsars are fantastic cosmic tools for scientists to study a wide range of phenomena.The light emitted by a pulsar carries information about these objects and what is happening inside them. That means pulsars give scientists information about the physics of neutron stars, which are the densest material in the universe (with the exception of whatever happens to matter inside a black hole). Under such incredible pressure, matter behaves in ways not seen before in any other environment in the universe. The strange state of matter inside neutron stars is what scientists call "nuclear pasta": Sometimes, the atoms arrange themselves in flat sheets, like lasagna, or spirals like fusilli, or small nuggets like gnocchi.
Some pulsars also prove extremely useful because of the precision of their pulses. There are many known pulsars that blink with such precise regularity; they are considered the most accurate natural clocks in the universe. As a result, scientists can watch for changes in a pulsar's blinking that could indicate something happening in the space nearby.
It was with this method that scientists began to identify the presence of alien planets orbiting these dense objects. In fact, the first planet outside Earth's solar system ever found was orbiting a pulsar.
Because pulsars are moving through space while also blinking a regular number of times per second, scientists can use many pulsars to calculate cosmic distances. The changing position of the pulsar means the light it emits takes more or less time to reach Earth. Thanks to the exquisite timing of the pulses, scientists have made some of the most accurate distance measurements of cosmic objects.
Pulsars have been used to test aspects of Albert Einstein's theory of general relativity, such as the universal force of gravity.
The regular timing of pulsars also may be disrupted by gravitational waves — the ripples in space-time predicted by Einstein and directly detected for the first time in February 2016. There are multiple experiments currently searching for gravitational waves via this pulsar method.
Using pulsars for these types of applications depends on how settled they are in their rotation (thus providing very regular blinks), Ransom said. All pulsars are slowing down gradually as they spin; but those used for precision measurements are slowing down at an incredibly slow rate, so scientists can still use them as stable time-keeping devices.
Comments
Post a Comment