The Disappearing Star

And now for the next trick, we will make a star disappear! Astronomers have just discovered a star in the Galaxy that is losing brightness fast.

Although generally stable, a star can and does vary in brightness every so slightly during the adult phase of its lifetime. A star can slowly increase in brightness as it builds up more nuclear fusion products in its stellar center. This happens to all stars. For the Sun this amounts to a 30 percent increase in brightness since it formed 4.5 billion years ago. Eventually, in another 1 billion years, the Sun will be so hot that it will boil away the oceans (but let us not digress).

Secondly, many stars brighten and fade on regular timescales of hours to years. These are wee brightness changes amounting to about 0.1 - 1 percent of the total flux on average, with some more extreme cases known especially for the smallest stars. There is one attribute I have not mentioned: stellar dimming. Stars cannot lose brightness.

This is why it is particularly interesting news that astronomer Tabetha Boyajian of Lousiana State University has recently discovered a star that has lost a whopping 15 percent of its total flux in the past century. There are very few plausible explanations.

It is tempting to say that the star is surrounded by a ring of gas and dust, as is typical of young stars, except that this star is middle-aged like the Sun. Also a ring of dust will shine in infrared light but this disk does not have any infrared signature. One could also posit that there is a giant swarm of comets in-falling into that inner star system, except then it would be hard to explain the sustained dimming over the past century.

There is even a bizarre idea floating around that it is a message from an alien civilization. Let’s not go there yet, as astronomers should fall back on such an explanation only after all else fails. The best idea at the moment is that it is swallowing a planet.

It is not uncommon for planets to “migrate” from the outer to inner parts of stellar system. In this scenario, a close (but not collisional) interaction of a star with another star can disrupt the orbit of a planet enough to send it hurling into its center. This would cause a temporary brightening of the star, followed by a relatively speedy recovery to its normal brightness. It is in this phase following the crash and before it has settled down again that we see Boyajian's star.

If so, then this is the first of its class. Perhaps astronomers will now be cued in to try to find other such examples of planets dying in this spectacular way, and eventually to witness a crash. Hopefully it will be from a safe distance.

Dr. Brenda Frye

About Dr. Brenda Frye

Brenda L. Frye is an observational cosmologist at the Department of Astronomy/Steward Observatory, University of Arizona. She earned her Ph. D. in Astrophysics from the University of California at Berkeley, assisted by a National Science Foundation Graduate Research Fellowship.

Her thesis work involved measuring the concentration of the total mass of visible plus dark matter in the fields of massive galaxy clusters, a program requiring the use of some of the largest telescopes in the world.

Moving a mile from her Ph. D. institution, she assumed a postdoctoral position with the Supernova Cosmology Project at Lawrence Berkeley National Laboratory under the direction of Professor Saul Permutter.

She then treked across the country to take a National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship and a Princeton Council on Sciences and Technology Fellowship both at Princeton University.

Moving further east, she became a Lecturer in Physics at Dublin City University in Dublin, Ireland, where a number of European collaborations were formed.

From there she crossed back across the pond to the west coast of the U. S. to become a tenure-track Assistant Professor of Physics at the University of San Francisco.

Her travels have now landed her at her Alma Mater in Tucson, where she teaches and does research. The aims of her research continue to be to use gravitational telescopes in space as 'lenses' to study the properties of dark matter and those of distant galaxies back to when the universe was <900 million years old.

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