- 4158 - PULSARS - radio beams coming from stars? A Pulsar is a pulsating radio source. It is a highly magnetized Neutron Star. It emits beams of radio electromagnetic radiation out of its poles. There is a bizarre pulsar just found that switches between two brightness modes. Astronomers finally figured out why.
-------------- 4158 - PULSARS - radio beams coming from stars?
- Pulsars are the lighthouses of the
universe. These rotating dead stars shoot twin jets of radiation from their
poles, usually with a predictable rhythm. But sometimes pulsars behave
strangely, and one pulsar in particular has had astronomers scratching their
heads for years. It’s called” PSR J1023+0038”, and a decade ago, it shut off
its jets and began oscillating between two brightness levels in an
unpredictable pattern. -
-
- Now, scientists think they understand why:
it is eating a neighboring star. When a
supergiant star approaches the end of its lifespan, it will explode and
collapse into a back hole if it has enough mass, or into a neutron star if it
does not.
-
- Neutron stars are the remaining,
ultra-dense cores of the old star. They are often very fast-spinning, and a
subset of them become pulsars. This Pulsar began life this way, and when it was
discovered in 2007, it behaved like a normal pulsar. But it didn’t stay that way?
-
- In 2013, something changed. The radio
pulses, evidence of its twin lighthouse beams , shut off. The was a sudden
explosion of energy at multiple wavelengths: gamma rays and X-rays increased by
a factor of five, and in visible light the star brightened by 1-2 magnitude.
Also it seemed to have formed an accretion disk: a hot swirling mass of
material surrounding the star.
-
- Perhaps most strangely, the star began
alternating between two intensities in X-ray wavelengths: a high mode and a low
mode, and it has continued like this over the entire decade since. It spends
about 70% of its time in high mode, the rest in low, and alternates between the
two every few seconds or minutes on an unpredictable schedule.
-
- Astronomers involved a dozen cutting-edge
ground-based and space-borne telescopes to learn more. These telescopes covered a gamut of
electromagnetic wavelengths, and with them, astronomers were able to piece
together what was going on.
-
- The accretion disk is made of matter being
pulled from the pulsar’s neighboring star. This matter, as it closes in on the
pulsar and begins to accumulate, is heated by the solar wind. The matter begins
to glow in X-ray, UV, and visible light, and the hot, glowing material is what
astronomers have been seeing as the pulsar’s ‘high mode.’ Eventually, there is
a process by which the matter is expelled at high energies, leaving
perpendicular to the accretion disc, in the direction of the pulsar’s jets.
-
-
Enormous amounts of matter, similar to cosmic cannonballs, are launched
into space within a very brief time span of tens of seconds. This violent expulsion results in the pulsar
returning to its ‘low mode,’ having removed the heated material from its
vicinity.
-
- Then the cycle repeats.
-
- The lessons learned from this weird pulsar
have taught us more about the physics of accretion, and that knowledge can now
be applied in the study of other unexplained variable phenomena, including the
accretion disks of some black holes.
-
-
September 18, 2023 PULSARS -
radio beams coming from stars? 4158
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