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---------------------- 2726 - MAGNETISM - throughout the Universe?
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- Magnetism is protecting us from harmful space radiation and preventing our atmosphere from being stripped away by solar winds. There is the Earth’s magnetic field that surrounds and protects our planet.
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- I remember first learning about Earth’s magnetic field in Boy Scouts. We magnetized a needle rubbing it with a magnet. Then, floated it is a dish of water riding on a cork. The needle always pointed in a north - south direction.
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- In observational astronomy today, these Earth’s magnetic poles are far less important than the geographic poles that we rely on to align our equatorially mounted telescopes. This is because the Earth’s magnetic poles are slowly moving away from true north.
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- Magnetism is what causes the Northern Lights. This magnetic blanket, Earth’s magnetic field, probably made life on this planet possible. Earth’s magnetic field’s origin lies in the electric currents that flow in the molten iron that makes up our planet’s outer core.
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- More distant, cosmic magnetic fields that are the reason that pulsars act like radio lighthouses and vast clouds of electrically conducting gas get sculpted into strange and unusual shapes.
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- Magnetic fields everywhere are created around moving charged particles. Magnetism is a force that is intimately related to electricity. Whenever an electric current flows there will be an associated magnetic field in the surrounding space. The movement of any charged particle will produce a magnetic field.
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- Try turning your stove burners on and off and see if your smartphone’s compass app can detect the magnetic field generated as the current runs through the cable. These fields always have a direction, which is why Earth has a north and a south pole.
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- When two magnetic fields come close to each other, they will try to align, potentially causing the physical objects causing them to move. A compass needle, like your needle floating on the cork, has a magnetic field, and so will always try to line up with Earth’s field and point north - south.
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- Similarly, the motion of a charged particle will change as it passes through a magnetized area, due to the interaction of the electric and magnetic fields.
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- How the direction changes depends on the charge and mass of the particle, the strength and direction of magnetic field and how fast the particle is traveling.
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- The Earth’s magnetic field envelops space and extends out to the Moon. For most of the time the Moon is inside the Earth’s magnetic field. It only pops out for a few days around the time of a New Moon.
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- When it does, the Moon moves into the solar wind, the Sun’s outer atmosphere that expands into space at a speed of a million miles an hour.
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- This solar wind can’t penetrate Earth’s magnetic field and instead slams straight into the Moon.
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- As the solar wind pushes against Earth’s magnetic field, it adds energy to it that accelerates charged particles down into our atmosphere. When the particles interact with atmospheric gas, they pass their energy on and cause the gas to glow, that we call the Northern Lights.
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- The solar wind is blocked from reaching our atmosphere because it too contains a magnetic field. When the gusty flow of magnetized plasma reaches the Earth’s magnetic field, it flows around it, causing it to move and ripple like a windsock in a breeze.
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- This property prevents the solar wind from reaching our atmosphere and stripping it away, as happened on Mars. It also provides us with protection from electrically charged cosmic rays. Cosmic Raya are charged particles that come to us from outer space.
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- This life-preserving property that planetary magnetic fields have means that it’s important to consider them when it comes to studying exoplanets. So far, we’re unable to directly observe an exoplanet’s magnetic field.
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- The discovery of the Sun’s magnetic field came in 1908 and was made by American astronomer George Ellery Hale.
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- In 1896, Dutch physicist Pieter Zeeman was carrying out experiments when he found that a strong magnetic field could affect the light given off by a “luminous vapour”. The spectral lines emitted by the vapor were broadened or, in extreme cases, split into several components. In a paper published in 1897, Zeeman suggested that his discovery might be used to detect cosmic magnetic fields.
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- Indeed, it was this technique that was used by Hale to detect the magnetic field of sunspots.
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- The Zeeman effect also polarizes the light in particular ways that can be used to understand the strength and direction of the distant magnetic fields, allowing astronomers to probe distant magnetism studying electromagnetic radiation.
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- In fact, the Sun allows us to investigate cosmic magnetism up close. Observations of the Sun provide a fantastic level of detail that shows us how dynamic stellar magnetic fields can be.
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- The Sun has an overall magnetic field that connects the north and south magnetic poles, which are close to the heliographic north and south poles, as they are on Earth.
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- Magnetic fields are created around moving charged particles. Flux ropes, magnetic fields arching between sunspots, can be revealed by the glowing, charged gas tracing their paths.
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- Closer inspection of the solar atmosphere reveals arches of magnetic field connecting pairs of sunspots and twisted magnetic field structures known as flux ropes.
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- These flux ropes are revealed because glowing, electrically charged gas traces them out, similar to the way iron filings sprinkled around a bar magnet align themselves to the field lines.
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- If you watch the Sun over time you’ll see that these magnetic structures are always changing and often erupt into the Solar System.
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- The Sun’s spatially resolved dynamic activity, powered by magnetism, gives us a glimpse of what other stars are also up to.
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- Pulsars are a sub-set of neutron stars. Formed from the collapsed cores of high-mass stars that have undergone a supernova explosion, they spin extremely rapidly. As they spin, they flash out pulses of radio waves, as if they were cosmic lighthouses. Some of them flash many times a second.
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- When Jocelyn Bell-Burnell discovered pulsars in 1967 they were viewed as curious objects and jokingly labelled LGM for Little Green Men. But the radio flashes can be understood if you combine a very rapidly spinning star with a strong magnetic field.
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- As a dying star collapses, its magnetic field is also drawn in with the material of the star itself, intensifying the field strength to a trillion times that of the Earth’s. The presence of the field causes charged particles to gyrate around the magnetic field lines and when this happens, radio waves can be created. The radio signal will be concentrated at the north and south magnetic poles of the neutron star.
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- The final ingredient in the making of a pulsar is to have an offset between the star’s axis of rotation and the axis connecting the magnetic poles. This means that as the neutron star spins, the radio beam will sweep across space and our radio telescopes can detect it.
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- In fact, neutron stars are record holders when it comes to magnetism: another sub-set of these stars harbor the strongest magnetic fields in the Universe, a thousand times stronger than that of the pulsars.
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- These objects are rather unsurprisingly known as “magnetars“. Scientists are watching these pulsars carefully to detect the rippling fabric of the cosmos. A pulsar’s beams sweep across space because the axis of its magnetic poles isn’t aligned with its axis of rotation.
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- Galactic magnetism The magnetic field of Earth and the magnetic field of the Sun, thanks to the solar wind, are not the only fields we find ourselves immersed in.
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- Our Galaxy, the Milky Way, has a magnetic field with a strength tens of thousands of times less than that of the Earth’s. What the galactic field does have in common with the Earth, though, is that rotation is at the heart of its existence.
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- Magnetic fields in astrophysical objects are created by dynamos, a mechanism in which the rotation of an electrically conductive liquid (such as the molten iron in the core of a planet) is converted into magnetic energy.
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- In this way, how fast an astronomical object spins is an important aspect of magnetic fields and dynamos. In this context we can understand why Earth has a relatively strong field whereas Mars, once thought to be more Earth-like than it is today, doesn’t.
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- Inside Earth, the rotating molten shell means its dynamo is still acting. Mars, on the other hand, had a dynamo, but it ceased acting when the interior of this smaller planet cooled and solidified, leaving only a remnant of its magnetic field locked up in its rocks.
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- When it comes to timescales, stars and planets can take anything from hours to weeks to complete a single rotation.
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- But these bodies have been around for so long that plenty of time has passed during their lifetimes to sustain and even evolve their magnetic fields.
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- The Sun rotates once every 27 days and has been around for 4.5 billion years. Assuming that the rotation rate has been constant, or on average, during all of this time, the Sun could have spun over 60 billion times.
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- This isn’t the case when it comes to galaxies though. Our Milky Way Galaxy rotates once every few hundred million years, which means there has only been time for it to make a few hundred rotations.
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- So, while a dynamo is important for our Galaxy, there are other additional processes that are making an impact and which still need to be understood.
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- In 2017, a team led by scientists from the Max Planck Institute for Radio Astronomy published work showing that galaxy observations can be used to investigate magnetic fields when the Universe was much younger.
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- Their study of a galaxy that is nearly five billion lightyears away allows us to look back into the early Universe to study the history and evolution of magnetic fields, providing insight into a question that astronomers have long wanted to answer: how long have magnetic fields existed for?
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- Magnetic fields are magnificent and common across the cosmos. From planets and stars, to galaxies and beyond.
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- Along with gravity, magnetism is responsible for shaping and controlling what we observe. So, next time you look up, no matter what you’re looking at, remember the invisible force that is helping shape our Universe.
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---------------------------------- The history of magnetic astronomy:
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- 1600 – William Gilbert, the first person to investigate magnetism using scientific methods, publishes his work in a volume titled “De Magnete“.
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- 1865 – Physics Professor James Clerk Maxwell publishes a paper in which he unifies the areas of electricity and magnetism into a single theory.
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- 1901 – Norway’s Kristian Birkeland begins building “Terrellas” (little Earths) to test his theory that the aurora are formed by electrons hitting Earth’s magnetic poles.
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- 1908 – American astronomer George Ellery Hale discovers magnetism on the Sun, providing the first evidence of magnetic fields beyond the Earth.
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- 1942 – Swedish physicist Hannes Alfvén theories that when a magnetic field threads through an electrically conducting gas, they become inseparable.
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- 2012 – After 35 years traveling through space, the Voyager 1 spacecraft finally exits the Solar System as it leaves the Sun’s vast bubble of magnetism behind.
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- April 30, 2020 2726
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