- 4330 - MAGNETIC STARS? - Why do Earth's magnetic poles flip? Every so often, Earth's magnetic poles completely flip. What causes this to happen? And how do these reversals affect life on Earth?
-------------------- 4330 - MAGNETIC STARS?
- Earth, our rocky, watery oasis in the
cosmos is the ideal place for life to flourish for a number of reasons. We sit at just the right distance from our
home star for liquid water to exist on the planet's surface.
-
- The gravitational pull of other large
planets helps protect us from collisions with wandering meteorites. And the
planet's magnetic field encircles Earth with a protective barrier that shields
us from charged particles hurtling through space.
-
- Earth's magnetic field is generated by the
complex flow of molten metallic material in the outer core of the planet. The
flow of this material is affected both by the rotation of Earth and the
presence of a solid iron core, which results in a dipolar magnetic field where
the axis roughly aligns with the rotational axis of the planet.
-
- Hidden in the chemical composition of
ancient rocks are clues that Earth's magnetic field is a dynamic, shifting
phenomena. Cooling magma rich in iron minerals is pulled into alignment with
Earth's magnetic field, similar to how a needle is pulled to point towards
north on a compass. The study of ancient geomagnetic fields recorded in rocks
is the subject of a discipline known as "paleomagnetism."
-
- “Paleomagnetic” research has provided
scientists with the knowledge that Earth's magnetic field has shifted and even
reversed in polarity many times in the geological past. But why? What causes the magnetic poles to flip?
-
- Earth's magnetic field varies at very short
timescales and extremely long ones, ranging from milliseconds to millions of
years. The interaction of the magnetic field with charged particles in space
can alter it at short timescales, while perturbations in the magnetic field at
longer timescales are caused by internal processes unfolding in the outer
liquid core of the Earth.
-
- Fluctuations in the magnetic field caused
by the movement of metallic material in the outer core have brought about full
reversals of the magnetic field's polarity in Earth's past.
-
- Paleomagnetic studies which have studied
previous states of the magnetic field have shown there are two possible states
of polarity, the current 'normal' state, where the lines of force of the field
enter towards the center of the Earth in the northern hemisphere and exit
towards the outside of the Earth in the southern hemisphere. The inverse, or
'reverse' polarity is also equally as probable and stable.
-
- Paleomagnetic studies have shown that
polarity reversals of Earth's magnetic field are not periodic and cannot be
predicted. This is largely because of the behavior of the mechanisms that are
responsible for it.
-
- The flow of the metallic fluid, mostly
molten iron, in the outer core of the Earth is chaotic and turbulent. Polarity
reversals occur during periods of low geomagnetic field intensity, during which
the intensity of the dipolar component drastically decreases, and the structure
of the field is unstable.
-
- The transitory period of polarity reversal
appears as a geologically instantaneous, with a duration spanning up to a few
thousand years.
-
- When the magnetic field is prone to
flipping, it is in a state of reduced intensity, resulting in a greater
exposure of Earth's atmosphere to solar wind and cosmic rays in the form of
charged particles.
-
- A recent study showed that during the
“Laschamps excursion”, a recent period of low magnetic field intensity which
occurred only 41,000 years ago, the global cosmic ray flux reaching the Earth's
atmosphere was up to three times higher than today's value.
-
- Currently, there is no significant evidence
of a correlation between mass extinctions of life on Earth and geomagnetic
polarity reversals. However, linking rates of species extinction and with
periods of low magnetic field intensity is hindered by uncertainties in the
known timescale of these magnetic 'flips'.
-
- Additionally, magnetic reversals happen
frequently on geological timescales (several hundred times in the past 160
million years), while recorded mass extinction events occur every hundred
million years or so much less frequently.
-
- In terms of human civilization, it is not
the shifting of the magnetic poles that is directly concerning, but the
resulting period of reduced geomagnetic field intensity. Society is growing
increasingly reliant on technology, and the effects of a reduced magnetic field
intensity should be seriously considered by international organizations.
-
- The risks to which our planet and
civilization is exposed could have significant impacts on civil society, how we
do commerce, security, communications, power infrastructure, satellites and the
lives of people in low Earth orbit. Unfortunately, the sporadic nature of
magnetic variations and reversals means we cannot predict when exactly this
will happen, all we know is that it will happen.
-
- A new cosmic object has been found that is
the most magnetic star in the universe.
The record-breaking find of a star 43,000 times more magnetic than the
sun could help unravel the mystery of how magnetars form.
-
- The star, known as “HD 45166”, has a unique,
helium-rich spectral signature that hints at an unusual origin. In addition to setting records, it might
represent the first stage in the lifecycle of a magnetar, a strange type of neutron
star.
-
- Neutron stars are the densest known
celestial objects in the universe, packing a sun's worth of mass into a ball no
wider than a city. Their highly magnetic versions magnetars have some of the
strongest known magnetic fields in the universe. Neutron stars and magnetars
form in the wake of massive supernova explosions, when the leftover material
from a dead star condenses back into an extremely dense, hot object.
-
- Astronomers are still trying to understand
what conditions produce magnetars versus regular neutron stars. Located 3,000 light-years from Earth in the
constellation Monoceros (the Unicorn), “HD 45166” has puzzled scientists for
more than a century. The star behaves similarly to a type of extremely bright
stellar object known as a Wolf-Rayet star, except that it is smaller, dimmer
and has an abnormally high concentration of helium.
-
- Using data from several ground
observatories, astronomers discovered that HD 45166 is extremely magnetic, a record-smashing
43,000 times more magnetic than the sun. The researchers suspect that, unlike
most massive helium stars, which evolve from red supergiants, HD 45166 formed
during a merger between two smaller stars. They also believe that in several
million years, it will explode into a modest supernova and re-form as a
magnetar.
-
- This proto-magnetar represents a new type
of stellar object never seen before, a
massive magnetic helium star.
-
-
January 10, 2023 MAGNETIC STARS? 4312
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--------------------- --- Monday, January 29,
2024
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