Old Stars’ Fossil Fields

Astronomers have confirmed that strong magnetic fields are frozen in place deep inside aging stars.
Stars like the Sun puff up and become red giants towards the end of their lives, so they’re much larger even though the masses don’t really change. The red giants (“old” Suns) of the same mass as the Sun do not show strong magnetic fields in their interior, but for stars slightly more massive, up to 60% host strong magnetic fields. University of Sydney
Stars create magnetic fields through convection, the swirling, Ferris-wheel-like motion of hot, ionized gas (or boiling water, for that matter). Where convection happens in a star depends on how massive the star is: low-mass stars, including the Sun, have convective outer envelopes around a non-convective core, but stars a little bulkier — up to a couple Suns’ worth — do have convective cores.
Recently, Jim Fuller (Caltech) and colleagues found that strong core magnetic fields could explain the oddly weak, on-and-off brightening behavior of a sample of red giant stars. These stars are low- to middle-mass and have stopped fusing hydrogen in their centers, so they don’t have convective hearts. They also often have a mismatched, variable glow, with one hemisphere brightening as the other fades. What was strange about the sample the team looked at was that this group didn’t vary as much in brightness as it should have.
Now, Dennis Stello (University of Sydney and Aarhus University, Denmark), Fuller, and their team has expanded this work to 3,600 red giants, observed with the Kepler spacecraft. The astronomers found that here, too, some red giants had “muffled” variations, but just how much they were suppressed depended on how massive the star was. For stars just above the Sun’s  mass and lighter, the stars looked normal. But for the heftiest of the sample — 1.6 to

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Brightest Supernova Baffles Astronomers

The most luminous supernova ever discovered, ASASSN-15lh, challenges a popular theory for blazingly bright exploding stars.
The left image shows the yellow-orange host galaxy prior to the supernova’s discovery, captured by the Dark Energy Camera. The righthand image, from Las Cumbres Observatory Global Network, shows the supernova, whose blue light outshines its host. The Dark Energy Survey / B. Shappee / The ASAS-SN Team
About six months ago, we alerted readers to the discovery of the most luminous supernova ever. Now the discovery team is releasing additional information, and it strains even the most extreme physical scenarios.
The explosion of light initially appeared in June 2015 as the faintest of dots in automated images taken by the All-Sky Automated Survey for Supernovae (ASAS-SN), which repeatedly observes the same areas of sky to look for ephemeral bursts of light. Sophisticated software spotted the sudden but subtle influx of light, prompting astronomers to go fishing for follow-up observations at several telescopes. They soon found that the light from the source, dubbed ASASSN-15lh, had traveled for 2.8 billion years to reach Earth.
Due to its distance, ASASSN-15lh only reached about 17th magnitude at its brightest, but its luminosity outshone any supernova yet discovered. Even months later, this single object continues to emit more energy per second than all the stars in the Milky Way.
This image shows two of the 14-cm telescopes used in the All-Sky Automated Survey for SuperNovae that discovered ASASSN-15lh. Wayne Rosing
Subo Dong (Peking University, China) and colleagues released an update to the discovery data in January 15th’s Science. Following a spate of follow-up spectra, the team continued to track the supernova’s goings-on using the Las Cumbres Observatory Global Telescope Network (LCOGT; see the October 2012 issue of Sky & Telescope for more on this ambitious project) and the Swift space telescope. The light curves

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