Magnetic Mystery Solved

ForteanTimes

Magnetars stars with magnetic fields a thousand million million times stronger than Earth's are formed when some of the biggest stars in the cosmos explode, says a team led by Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics.

The astronomers base their conclusions on a study made with CSIRO's Australia Telescope Compact Array and Parkes radio telescope in eastern Australia.

''The source of these very powerful magnetic objects has been a mystery since the first one was discovered in 1998,'' says Gaensler.

''Now we think we¹ve nailed it.''

http://www.spaceref.com/news/viewpr.html?pid=16011

... How can you determine the strength of a star's magnetic field?
(i.e., a distant one, not the Sun)

There's an effect called Zeeman splitting that allows people to determine the strength of a star's magnetic field. When you spread a star's light out in a spectrograph (which is very much like a prism), in addition to a rainbow of colors, you'll also see thin, dark lines. These are called absorption lines, and each one is due to atoms of a particular element in a star's outer layers.

When a magnetic field is present, each single line splits into a series of lines. The number of lines in each set and the distance between them depend on the properties of the elements involved, but they also depend on the strength of the star's magnetic field. Astronomers measure the spectral absorption lines to deduce the magnetic field strength.

The same thing happens when a magnetic field is applied to hot gas in a laboratory setting.

I'd come across absorption lines but didn't realise that they could
vary due to the magnetic field. Learn something every day round here!
:hi:

That's very cogent. Are you an astronomer? A teacher?

I figure if I reach a point where I can't explain astronomy clearly to people -- a weakness that afflicts a lot of professional astronomers -- I need to re-evaluate my priorities.

My rudimentary grasp of that was greatly illuminated. Thanks.

Is there someone else around here who enjoys Fortean Times?