Thursday, July 28, 2016

GJ 3253: Astronomers Gain New Insight into Magnetic Field of Sun and its Kin

Illustration of Low-mass Star
An artist's illustration depicts the interior of a low-mass star, such as the one seen in an X-ray image from Chandra in the image below. Such stars have different interior structures than our Sun. A new study looking at four of these low-mass stars shows the strength of magnetic fields of these stars - which is revealed by the amount of X-ray emission from the stars - are similar to those of more massive ones like the Sun. This discovery may have profound implications for understanding how the magnetic field in the Sun and stars like it are generated.  (Credit: NASA/CXC/M.Weiss)

Illustration of Sun-like star
 This artist's impression shows the internal structure of the sun and stars with a similar mass to the sun. These stars have a divided internal structure with an inner radiation zone, where energy moves outward, and an outer convection zone shown by loops with arrows. 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. A difference in the speed of rotation between the radiation and convection zones was thought to generate most of the magnetic field in the sun by causing magnetic fields along the border between the two zones to wind up and strengthen.  Credit: NASA/CXC/M.Weiss).  More Images 

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.

The Sun and stars with approximately the same mass have a divided internal structure with an inner radiation zone (energy moves outward) and an outer convection zone (the energy circulates). Stars with significantly lower masses, however, do not have such a differentiated structure. Instead, the process of convection is dominant throughout the star, which is depicted in the artist's illustration in the main panel of the graphic.

The researchers in this latest study looked at four low-mass stars - two with Chandra and two with archival data from the ROSAT satellite - and found their X-ray emission was similar to that of stars like the Sun. (The inset in the graphic shows Chandra's data of one of these low-mass stars, GJ 3253).

This result was surprising because many scientists think the boundary between the radiation and convection zones in the Sun and Sun-like stars contributes to the strength of its magnetic field. If stars without such a boundary have relatively powerful magnetic fields, then this theory may need to be re-examined.

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.

Fast Facts for GJ 3253:

Credit X-ray: NASA/CXC/Keele Univ/N.Wright et al; Illustration: NASA/CXC/M.Weiss
Scale: X-ray image is 20 arcsec across (about 0.003 light years)
Category: Normal Stars & Star Clusters
Coordinates (J2000): RA 03h 52m 41.70s | Dec +17° 01’ 05.70"
Constellation: Taurus
Observation Date: 25 Sep 2013
Observation Time: 5 hours 45 min.
Obs. ID: 14603
Instrument: ACIS
References: Wright, N. et al, 2016, Nature (accepted)
Color Code: X-ray (Pink)
About: 31 light years (z=0.003)