Young protostar lights up the sky with X-ray bursts

Young protostar lights up the sky with X-ray bursts

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We have accumulated considerable knowledge about the mechanics and behaviors of stars, but there is much we still do not know. Oftentimes, we have to wait until a combination of good fortune and advancing technology open a window on new stellar phenomena we have yet to observe closely. Thanks to space-based X-ray telescopes, a “proto-star” in the constellation Orion is giving us just such an opportunity.

V1647 Orionis is a young star still surrounded by a circumstellar disk of gas that hasn’t undergone the self-sustaining fusion reactions that mark a star’s arrival on the Main Sequence; observation of the star suggests that it is perhaps a million years old. What is remarkable about this protostar is that observations from three X-ray space telescopes have been able to observe a northern and southern “hotspot” where the gas, drawn in towards the star by gravity, impacts the stellar surface.

Interaction between the star’s magnetic fields and the gas combined with the high velocity of the gas, approximately 2000 kilometers per second, causes a dramatic reaction, heating these areas to 50 million degrees Celsius (as a point of comparison, the core temperature of our own Sun is believed to be about 15 million degrees Celsius and the rest of the star’s surface averages 6500 degrees Celsius).

As a matter of fact, the star first attracted attention in 2003 when just such an outburst increased its X-ray luminosity by 100 times and illuminated a surrounding dust cloud, “forming” McNeil’s Nebula. Correlation with a few other young stars shows a similar pattern of X-ray bursts, suggesting that the accretion process may progress in spurts rather than a smooth, continuous gaining of mass. David Weintraub, a member of the study team, suggested that, in a way similar to the Sun’s X-ray flares and violent solar activity, a “continual cycle of shearing and reconnection” of magnetic field lines could be causing the X-ray outbursts.

Careful observation of the star’s X-ray luminosity using multiple observations from three different telescopes, JAXA’s Suzaku, NASA’s Chandra, and the ESA’s XMM-Newton, also allowed the determination of the star’s rate of spin at a revolution per day, an observation in line with the star’s stage in the stellar life cycle. This rapid spin, combined with the slower spin rate of the disk of gas, would cause just such an interplay of magnetic fields as described above. Hopefully, further observation will shed light on the early life of stars; perhaps some of those insights will also tell us more about the extreme behavior of our Sun, as well.

 

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