- 4268 - GAMMA RAY PULSARS. Scientists have been able to both discover and analyze the timing behavior and spectra of many of these newfound pulsars to further our understanding of these exotic stars that we are able to use as cosmic clocks.
------------------------- 4268 - GAMMA RAY PULSARS
- This gamma-ray pulsar milestone inspires
innovative astrophysics.
The Naval Research Laboratory,
in conjunction with the international Fermi Large Area Telescope Collaboration,
announce the discovery of nearly 300 gamma ray pulsars. This milestone comes 15
years after the launch of Fermi in 2008 when there were fewer than ten known
gamma-ray pulsars.
-
- Pulsars are formed when massive stars have
burned through their fuel supply and become unable to resist the inward pull of
their own gravity. This results in the star collapsing into a dense, spinning,
magnetized neutron star. Their spinning magnetic fields send out beams of gamma
rays, the most energetic form of light.
-
- As these beams sweep across the Earth, the
highly sensitive Fermi gamma-ray telescope can observe their periodic energy
pulses. Fermi has more than 15 years of data.
-
- They began as young pulsars in a binary
system. Like a spinning top, they eventually slowed down and became inert. Over
the past hundreds of millions of years, their binary companions dumped matter
onto them, causing their speed to increase again, very dramatically and far
faster than before. These high-speed
MSPs are now some of Nature's most precise timekeepers.
-
- Scientists have been using these cosmic
clocks in experiments called “Pulsar Timing Arrays”. By searching for tiny
deviations in the times at which the pulses arrive, scientists have been able
to search for ripples in spacetime.
-
- These ripples, known as “gravitational
waves”, are produced when very massive objects, like pulsars, accelerate very
quickly. Very strong gravitational wave sources indicate a cataclysmic crash of
dense, compact objects such as neutron stars and black holes.
-
- Several pulsar timing array collaborations
provide the first compelling evidence for very low-frequency gravitational
waves, likely from the merger of supermassive black holes. These low-frequency gravitational waves allow
us to peer into the centers of massive galaxies and better understand how they
were formed.
-
- The pulsar timing array results have
critical practical applications. The spacetime distortions set a limit on how
precisely we can use pulsars for critical navigation and timing. In
pulsar-based navigation, these spinning pulsars play much the same role as GPS
satellites do, but we are able to use them far beyond the Earth's orbit. Now we know where that ultimate stability
limit is.
-
- Gravitational waves, unlike radio waves,
which are bent like the light in a prism as they travel to earth, the gamma
rays shoot straight to us. This reduces potential systemic measurement errors.
-
- Something similar can happen when a neutron
star and its binary companion are very close to each other and the 'recycling'
process. The intense radiation and particle wind from the pulsar eats away at
the surface of the other star, resulting in a puffball of evaporated material.
-
- When compared to radio observations, Fermi
is particularly adept at finding these "spiders" as, in many cases,
radio waves are eclipsed as the pulsar beam passes the remnants of the
companion star. Gamma rays, however, are capable of passing right through.
-
-
December 12, 2023 4268
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--------------------- --- Tuesday, December 12,
2023
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