Astronomers gain new insight into magnetic field of Sun and its kin

July 27, 2016, Chandra X-ray Center
Magnetic fields on the Sun and stars like it are responsible for much of their behavior, including the generation of powerful storms that can produce spectacular auroras on Earth, damage electrical power systems, knock out communications satellites, and affect astronauts in space. As discussed in our latest press release, new research relying on data from NASA's Chandra X-ray Observatory is helping astronomers better understand how these magnetic fields are produced. By comparing the X-ray emission, an excellent indicator of a star's magnetic field strength, between low-mass stars and the Sun, a pair of astronomers was able to find an important clue about how stellar magnetic fields are generated. Credit: X-ray: NASA/CXC/Keele Univ/N.Wright et al; Illustration: NASA/CXC/M.Weiss

Astronomers have used data from NASA's Chandra X-ray Observatory to make a discovery that may have profound implications for understanding how the magnetic field in the Sun and stars like it are generated.

Researchers have discovered that four old with masses less than half that of the Sun are emitting X-rays at a much lower rate than expected.

X-ray emission is an excellent indicator of a star's magnetic field strength so this discovery suggests that these have much weaker magnetic fields than previously thought.

Since young stars of all masses have very high levels of X-ray emission and , this suggests that the magnetic fields of these stars weakened over time. While this is a commonly observed property of stars like our Sun, it was not expected to occur for low-mass stars, as their internal structure is very different.

The Sun and stars like it are giant spheres of superheated gas. The Sun's magnetic field is responsible for producing sunspots, its 11-year cycle, and powerful eruptions of particles from the solar surface. These solar storms can produce spectacular auroras on Earth, damage electrical power systems, knock out communications satellites, and affect astronauts in space.

"We have known for decades that the magnetic field on the Sun and other stars plays a huge role in how they behave, but many details remain mysterious," said lead author Nicholas Wright of Keele University in the United Kingdom. "Our result is one step in the quest to fully understand the Sun and other stars."

The rotation of a star and the flow of gas in its interior both play a role in producing its magnetic field. The rotation of the Sun and similar stars varies with latitude (the poles versus the equator) as well as in depth below the surface. Another factor in the generation of magnetic field is . Similar to the circulation of warm air inside an oven, the process of convection in a star distributes heat from the interior of the star to its surface in a circulating pattern of rising cells of hot gas and descending cooler gas.

Convection occurs in the outer third (by radius) of the Sun, while the hot gas closer to the core remains relatively still. There is a difference in the speed of rotation between these two regions. Many astronomers think this difference is responsible for generating most of the magnetic field in the Sun by causing magnetic fields along the border between the convection zone and the core to wind up and strengthen. Since stars rotate more slowly as they age, this also plays a role in how the magnetic field of such stars weakens with time

"In some ways you can think of the inside of a star as an incredibly complicated dance with many, many dancers," said co-author Jeremy Drake of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "Some dancers move with each other while others move independently. This motion generates magnetic field, but how it works in detail is extremely challenging to determine."

For stars much less massive than the Sun, convection occurs all the way into the core of the star. This means the boundary between regions with and without convection, thought to be crucial for generating magnetic field in the Sun, does not exist. One school of thought has been that magnetic field is generated mostly by convection in such stars. Since convection does not change as a star ages, their magnetic fields would not weaken much over time.

By studying four of these low-mass red dwarf stars in X-rays, Wright and Drake were able to test this hypothesis. They used NASA's Chandra X-ray Observatory to study two of the stars and data from the ROSAT satellite to look at two others.

"We found that these smaller stars have magnetic fields that decrease as they age, exactly as it does in stars like our Sun," said Wright. "This really goes against what we would have expected."

These results imply that the interaction along the convection zone-core boundary does not dominate the generation of in stars like our Sun, since the low mass stars studied by Wright and Drake lack such a region and yet their magnetic properties are very similar.

A paper describing these results by Wright and Drake appears in the July 28th issue of the journal Nature. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

Explore further: Mysterious, massive, magnetic stars

More information: Solar-type dynamo behaviour in fully convective stars without a tachocline, Nature, DOI: 10.1038/nature18638

Related Stories

Mysterious, massive, magnetic stars

September 11, 2015

A Canadian PhD student has discovered a unique object – two massive stars with magnetic fields in a binary system. Matt Shultz of Queen's University, Ontario, Canada found the system – Epsilon Lupi – and will publish ...

Magnetic fields on solar-type stars

December 12, 2014

The Sun rotates slowly, about once every 24 days at its equator although the hot gas at every latitude rotates at a slightly different rate. Rotation helps to drive the mechanisms that power stellar magnetic fields, and in ...

Other suns got the right spin

May 17, 2016

Astrophysicists from the Leibniz Institute for Astrophysics Potsdam (AIP) and the Johns Hopkins University in Baltimore have for the first time measured the rotation periods of stars in a cluster nearly as old as the sun ...

Recommended for you

Tiny 'water bears' can teach us about survival

March 20, 2019

Earth's ultimate survivors can weather extreme heat, cold, radiation and even the vacuum of space. Now the U.S. military hopes these tiny critters called tardigrades can teach us about true toughness.

A decade on, smartphone-like software finally heads to space

March 20, 2019

Once a traditional satellite is launched into space, its physical hardware and computer software stay mostly immutable for the rest of its existence as it orbits the Earth, even as the technology it serves on the ground continues ...

Researchers find hidden proteins in bacteria

March 20, 2019

Scientists at the University of Illinois at Chicago have developed a way to identify the beginning of every gene—known as a translation start site or a start codon—in bacterial cell DNA with a single experiment and, through ...

Turn off a light, save a life, says new study

March 20, 2019

We all know that turning off lights and buying energy-efficient appliances affects our financial bottom line. Now, according to a new study by University of Wisconsin-Madison researchers, we know that saving energy also saves ...

17 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

cantdrive85
1.4 / 5 (10) Jul 28, 2016
Whaaatt? You mean predictions don't match observations? How can that be?
ursiny33
2 / 5 (4) Jul 28, 2016
They can't even conceive that in the heart of the core , fusion doesn't stop with iron, fusion is a process thats once it starts the end game is to make all the elements it can, untill the heat and pressure and electron exchange can not sustain the construction of the final element (93) and it comes apart and piles up neutrons in the core, which becomes a secondary heat producing process outside of fusion, that lead to fusion of those neutrons into particle plasma
ursiny33
2 / 5 (4) Jul 28, 2016
In there light spectrum of stars, and it showing the dominant element iron ,and they can't measure the minor interior elements and neutrons in that light spectrum just the most dominant signature that why there compression stops in star core theory, at iron the process of fission has an end game it doesn't have a conscious or mechanical process to stop the process of fusion even if the star novas
ursiny33
2 / 5 (4) Jul 28, 2016
The mechanical end game of fusion is to build a neutron core to give birth to a neutron star which only happens a small percentage of the time because to the element make up of the star in just right element percentages
ursiny33
2 / 5 (4) Jul 28, 2016
It is a mechanical impossibility to construct a 30,000 square mile neutron star from a nova in 30 minutes or a hour or day, its is constructed over millions of years in a star the nova just gives it ,its final compression and imprints a crust layer of iron atoms on its surface, which makes it possible for the neutron star to have a surface magnetic field with electron exchange off those iron atoms on its surface and so its a finite number of iron atoms that can only exchange so many electrons even at the speed of light when the stars gravity holds way more electrons in orbit around it that can be exchange in its main field, it constitutes a shroud halo field in orbit around its main field making it a dual field star
ursiny33
2 / 5 (4) Jul 28, 2016
Super high temperatures diminish the magnetic field strength of orbiting electrons on atoms making kinetic collisions between electrons produce electron exchange easy
Maggnus
3.9 / 5 (7) Jul 28, 2016
Whaaatt? You mean predictions don't match observations? How can that be?

Spoken like someone who truly has no idea how the scientific method works. OH - look who it is!

Hey Acolyte - what did the EU predict about this? Hmm, ya - nothing.

Science progresses by making predictions about phenomena, by observations of those phenomena, and by seeing whether the predictions can be falsified.

The EU's way of going about this is to shout very loudly that their "theories" are right, even though they make no quantitative predictions at all - and hence cannot be falsified - and all the while stopping up their ears so as not to be able to hear any counter-arguments.

Science needs falsification in order to grow. The EU and other nutjob, ahem, philosophies abhor falsification.
I cannot say it better, thank you FSC.
ursiny33
2 / 5 (4) Jul 30, 2016
When an electron leaves a pole on the star, makes its big arc and enters the opposite pole ,that electron does not travel straight thru again for a long time because it get stuck orbiting an atom and bumps an electron to another atom in a chain reaction where a new electron exits off an atom in the magnetic field its called electron exchange, and if the star has a lot of ferrite iron atoms the bigger the magnetic field,
epoxy
Jul 30, 2016
This comment has been removed by a moderator.
Maggnus
3.4 / 5 (5) Jul 30, 2016
The 11-year cycle is driven just with convection of solar plasma around center of mass of solar system, so it's driven with position of Jupiter planet
No, it is not
(and another ones in smaller extent, even the Earth leaves its footprint in solar activity - it's indeed much lighter than Jupiter, but also much closer)
You are trying to conflate radial velocity with magnetic field flux. Even the Acolyte would argue with this bs. Stop it. Just, stop it.
. It's an effect analogous to Coriolis force at the Earth.
No, it is not.

quack quack quack.
Maggnus
3.4 / 5 (5) Jul 30, 2016
ferrite iron
**face palm** Says pretty much everything you need to know about this one.
epoxy
Jul 30, 2016
This comment has been removed by a moderator.
epoxy
Jul 30, 2016
This comment has been removed by a moderator.
barakn
4.3 / 5 (6) Aug 01, 2016
So try to argue it yourself. Jupiter shifts barycenter of solar system by about one solar radii, i.e. 742,000 km. Earth is smaller but more dense and also more close to Sun, so it wobbles it by some 449 km. -zephir
Barycenter is just a fancy word for center of mass, and while providing a convenient non-inertial frame of reference, there's nothing magic about it. Considering that the sun is responding without resistance to the gravity of the planets, it is following a straight line in curved spacetime. The only thing that might have an affect is the difference in a planet's force of gravity from one side of the sun to the other, i.e. the tidal force. It's been many years since I've bothered to calculate this, but the planets raise tides on the sun on the order of a few millimeters high, i.e. utterly insignificant. Your "theory" is simply astrology dressed up in fancy clothes.
barakn
3 / 5 (4) Aug 01, 2016
Meant to say "inertial," not "non-inertial."
torbjorn_b_g_larsson
3 / 5 (4) Aug 01, 2016
This should be good news for the habitability of M stars.

M stars are often claimed to be riddled with flares and CMEs, with ~ 10 % very calm ones and some wild "flare stars".

CME activity is statistically tied to flare activity, and flare stars have large average magnetic fields (and large X-ray activity). [ https://en.wikipe...ar_flare ; https://en.wikipe...are_star ]

So we may be tied to observation bias, with old M stars being calm. If a planet start out with a thick enough atmosphere and/or geodynamo field to have a Goldilock dense atmosphere as Earth (no Mars, no Neptune), it could eventually become and stay habitable for a long time.

gculpex
not rated yet Sep 18, 2016
only theory that the inner core is rotating.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.