User:Gryllida/Wikinews interviews astronomers who discovered smallest known star

January 13, 2018

prepared Develop

Known facts
WHEN: July 2017

WHO: astronomers at the University of Cambridge in England

WHAT: announced the discovery of a dwarf star. This star is known as EBLM J0555-57Ab. This star is slightly bigger than Saturn and smaller than Jupiter. The study was published in the journal Astronomy & Astrophysics. The star belongs to the Milky Way galaxy and is approximately 600 light years away from Earth. Its mean radius is about 80 percent the size of the largest planet in the Solar System, Jupiter, but despite its small size it is very dense. Its mass is almost 85±4 times the gas giant, the study said. The star's surface gravitational pull is about eleven times stronger than the Sun's — 300 times the strength by which the Earth attracts matter. It is part of a binary star system, meaning it moves around the galaxy with another star, both orbiting around the same central point. However, it stays so close to its companion star, that it takes about 7.8 days to orbit around the pair's shared centre. The distance between the two stars is less than between Mercury and the Sun, and about eight percent of an astronomical unit, in stark contrast to the 100–1000 astronomical units that typically separates two stars in such a system.

According to lead author of the study, Alexander von Boetticher, their "discovery reveals how small stars can be." He added, "Had this star formed with only a slightly lower mass, the fusion reaction of hydrogen in its core could not be sustained, and the star would instead have transformed into a brown dwarf". A brown dwarf converts hydrogen to deuterium, a hydrogen isotope, rather than helium, which is the usual result of such a process from most stars including the Sun.

The tiny star's temperature is lesser than most known gas giant exoplanets. "That star likely represents the smallest natural fusion reactor that we know of[...] We're trying to replicate fusion on Earth in labs, but that's basically as small as it gets in nature", Triaud told CBC News. The size of the star makes it difficult to study, but the brightness of its companion star also makes it more challenging. "It's like trying to look at a candle beside a lighthouse," Triaud said.

HOW: It was found using data from an array of automated telescopes called the Wide Angle Search for Planets (WASP). It was discovered by the method called "astronomical transit". This method is used to discover planets or satellites, and the astronomers initially thought it was merely an exoplanet. During a planet's revolution, when it crosses its parent star, there is a dip in the brightness of the light coming from the parent star. The companion of this dwarf is the size of the Sun, and it is brighter than the dwarf, making the discovery more difficult. "Indeed, until we measured the mass it looked just like a transiting planet", Amaury Triaud, co-author of the paper, told Popular Mechanics. With a brightness 2000 to 3000 times fainter than the Sun, it was the mass that indicated it was actually a dim star.

"After identifying a periodic photometric signal received by WASP, we obtained CORALIE spectroscopic radial velocities and follow-up light curves with the Euler and TRAPPIST telescopes. From a joint fit of these data we determine that EBLM J0555-57 consists of a sun-like primary star that is eclipsed by a low-mass companion, on a weakly eccentric 7.8-day orbit. Using a mass estimate for the primary star derived from stellar models, we determine a companion mass of 85 ± 4M Jup (0.081M ? ) and a radius of 0.84 +0.14 −0.04 R Jup (0.084R ? ) that is comparable to that of Saturn. EBLM J0555-57Ab has a surface gravity logg 2 = 5.50 +0.03 −0.13 and is one of the densest non-stellar-remnant objects currently known. These measurements are consistent with models of low-mass stars." (from publication abstract)

WHY: the researchers were looking into their equipment and saw an unusual flash of brightness

Questions

 * 1) What prompted your curiosity in the star? Was it a part of regular monitoring by an equipment? Was the brightness detected by a human or only by a computer at first?
 * 2) In the paper, you start the observations with the fact that WASP observed a source "between 2008-09-29 and 2012-03-22". What causes the observations to span across such a long time frame?
 * 3) What should "1SWASPJ055532.69-571726.0 (EBLM J0555-57, J0555-57 for brevity)" tell the reader? What does the name refer to? What information did this source include?
 * 4) In the abstract it is stated that the Euler (on the night of 2014-02-24) and TRAPPIST (on the night of 2015-12-23) telescopes were used to obtain additional data. Later in the paper, it is written that eclipse observations were made by these telescopes. Both these telescopes obtained an image in the z` band, correct? What is the z` band, and why is it used in these observations?
 * 5) The "eclipse" observations requirement is that the Earth must located between the Sun and the star, for the purpose of visibility of the star in the sky -- is this correct?
 * 6) What other equipment was used to obtain data about the star?
 * 7) After obtaining data, you analyzed it using several computational models, including, for instance, a wavelet-based Monte Carlo method for spectral analysis, ELLC star model for obtaining the geometric parameters of the system, MCMC sampler for uncertainty estimation. Would you be able to provide a complete list, and the role of each of these models, in a brief summary? Which of these computations was the most time-consuming? What computer (or supercomputer) did you use for performing these calculations?
 * 8) What is the discovered star size? How does it compare with the smallest theoretically possible star size, if that exists?
 * 9) What other activities -- in addition to the above described detection of the brightness -- were involved in the study?
 * 10) How were the measurements and calculations made to verify that the star was not an exoplanet? How long did these calculations take?
 * 11) Is the new star visible in any equipment right now? What is a planet revolution and 'crosses with parent star' process?
 * 12) What researchers participated in the study?
 * 13) How did you give a name to the star?
 * 14) What was the most time-consuming activities as a part of this research?
 * 15) Do you have plans on future work with the discovered star?
 * 16) Would you like to provide photos and images of the lab equipment, the research group, or the star itself?