Posts Tagged ‘binary stars’

Delta Cephei’s Hidden Companion

Bow shock around star Delta Cephei. Credit: NASA/JPL-Caltech/M

Bow shock around star Delta Cephei. Credit: NASA/JPL-Caltech/M

To measure distances in the universe, astronomers use cepheids, a family of variable stars whose luminosity varies with time. Their role as distance calibrators has brought them attention from researchers for more than a century. While it was thought that nearly everything was known about the prototype of cepheids, named Delta Cephei, a team of researchers at the University of Geneva (UNIGE), the Johns Hopkins University, and the European Space Agency (ESA), have now discovered that this star has a hidden companion. They have published an article about the discovery in The Astrophysical Journal.

Delta Cephei, prototype of the cepheids, which has given its name to all similar variable stars, was discovered 230 years ago by the English astronomer John Goodricke. Since the early 20th century, scientists have been interested in measuring cosmic distances using a relationship between these stars’ periods of pulsation and their luminosities (intrinsic brightness), discovered by the American Henrietta Leavitt. Today, researchers from the Astronomical Observatory of UNIGE, Johns Hopkins University and the ESA show that Delta Cephei is, in fact, a double star, made up of a cepheid-type variable star and a companion that had thus far escaped detection, probably because of its low luminosity. Yet, pairs of stars, called binaries, complicate the calibration of the period-luminosity relationship, and can bias the measurement of distances. This is a surprising discovery, since Delta Cephei is one of the most studied stars, of which scientists thought they knew almost everything.

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NASA Observatories Take An Unprecedented Look Into Superstar Eta Carinae

January 8, 2015 Leave a comment

Image Credit:  NASA, ESA, and the Hubble SM4 ERO Team

Image Credit:
NASA, ESA, and the Hubble SM4 ERO Team

Eta Carinae, the most luminous and massive stellar system within 10,000 light-years of Earth, is known for its surprising behavior, erupting twice in the 19th century for reasons scientists still don’t understand. A long-term study led by astronomers at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, used NASA satellites, ground-based telescopes and theoretical modeling to produce the most comprehensive picture of Eta Carinae to date. New findings include Hubble Space Telescope images that show decade-old shells of ionized gas racing away from the largest star at a million miles an hour, and new 3-D models that reveal never-before-seen features of the stars’ interactions.

“We are coming to understand the present state and complex environment of this remarkable object, but we have a long way to go to explain Eta Carinae’s past eruptions or to predict its future behavior,” said Goddard astrophysicist Ted Gull, who coordinates a research group that has monitored the star for more than a decade.

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UCLA Astronomers Solve Puzzle About Bizarre Object At The Center Of Our Galaxy

November 3, 2014 Leave a comment

For years, astronomers have been puzzled by a bizarre object in the center of the Milky Way that was believed to be a hydrogen gas cloud headed toward our galaxy’s enormous black hole.

Having studied it during its closest approach to the black hole this summer, UCLA astronomers believe that they have solved the riddle of the object widely known as G2.

A team led by Andrea Ghez, professor of physics and astronomy in the UCLA College, determined that G2 is most likely a pair of binary stars that had been orbiting the black hole in tandem and merged together into an extremely large star, cloaked in gas and dust — its movements choreographed by the black hole’s powerful gravitational field. The research is published today in the journal Astrophysical Journal Letters.

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Binary Stars Are More Common Than We Thought

High-mass stars are rarely solitary. This is what Bochum’s astronomers found out at the Ruhr-Universität’s (RUB’s) observatory in Chile. For several years, they observed 800 celestial objects that are up to one hundred times heavier than our sun. More than 90 per cent have turned out to be multiple systems. These data support the theory that heavy stars are already formed as twins.

Even with the world’s largest telescopes, binary stars cannot generally be distinguished as two discrete points. In order to prove their existence nevertheless, the team headed by Prof Dr Rolf Chini from the RUB Institute of Astronomy used a trick. They watched the celestial bodies over a period of many weeks and months and detected that their spectra and their brightness oscillated. Regular brightness variations occur if two or more stars pass each other again and again. These long-term measurements were possible only because the Ruhr-Universität operates its own observatory in the best place for astronomical observations worldwide: the Atacama Desert in Chile.

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‘Upside-Down Planet’ Reveals New Method For Studying Binary Star Systems

Simulation. Credit: NASA

Simulation. Credit: NASA

What looked at first like a sort of upside-down planet has instead revealed a new method for studying binary star systems, discovered by a University of Washington student astronomer.

Working with UW astronomer Eric Agol, doctoral student Ethan Kruse has confirmed the first “self-lensing” binary star system — one in which the mass of the closer star can be measured by how powerfully it magnifies light from its more distant companion star. Though our sun stands alone, about 40 percent of similar stars are in binary (two-star) or multi-star systems, orbiting their companions in a gravitational dance.

Kruse’s discovery confirms an astronomer’s prediction in 1973, based on stellar evolution models of the time, that such a system should be possible. A paper by Kruse and Agol was published in the April 18 edition of Science.

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NOAO: A Sharp Eye On Southern Binary Stars

Unlike our sun, with its retinue of orbiting planets, many stars in the sky orbit around a second star. These binary stars, with orbital periods ranging from days to centuries, have long been the primary tool for measuring basic quantities like the star’s mass. While masses of normal stars are now well determined, some binaries present special interest because their stars are unusual (e.g. very young) or because they may contain planets, gas clouds, or other stars.

Now, astronomers at the Cerro Tololo Inter-American Observatory (CTIO) and at the US Naval Observatory (USNO) are making use of the latest technology, speckle imaging, to measure the separation of close binary stars. By observing them over a period of years, their obits have been determined with exquisite precision.

Using the new speckle camera at the 4.1-m Southern Astrophysical Research Telescope (SOAR) in Chile with its novel electron-multiplication CCD detector, the team is able to measure the angular separation of stars down to 25 milli arcseconds: this is equivalent to measuring the size of a quarter atop the Empire State building in New York – from Washington, DC. This is over 2000 times better than the human eye can resolve. As Dr. Andrei Tokovinin, the lead author on the paper, said: “This camera surpasses adaptive-optics instruments at the 8-m telescopes, which work in the infrared and can only resolve binaries wider than 50 milli arcseconds.“

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Two Suns Are Probably Better Than One, Or Not?

An International Collaboration of FACom researchers and Astronomers of the University of Texas (El Paso) and New Mexico State University, have discovered a physical mechanism that could make binary stars more hospitable to habitable planets than single stars. The discovery could imply a modification in the estimations of the number of planets potentially harboring life in the Galaxy and in the future selection of targets for the search of life elsewhere.

Habitability is the term astronomers use for referring to the general condition a planet must fulfill in order to be suitable for life. It has been customary to think that habitability is determined mainly by the amount of light a planet receives from its host star. If the planet receives too much light it is too hot and water will be boiling in its atmosphere (if it has one!). On the other hand, if the planet is too far and light from the star shines weakly, the surface is too cold and water becomes frozen. In the middle between these extremes lies the so called “radiative habitable zone” also nicknamed the “Goldilocks Zone”.

But planets in the Goldilocks Zone need to meet other conditions to be considered actually habitable. One of the most important is having a dense and wet atmosphere where heat could be trapped and water could condensate at the surface. But preseving an atmosphere is a real challenge for a young planet.

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Astronomers Team Up With The Public To Solve Decade Old Puzzle

An extremely precise measurement of the distance to a star system has finally allowed astronomers to solve a decade-old puzzle, confirming understanding of the way exotic objects like black holes interact with nearby stars.

Published today in prestigious journal Science, a team of astronomers headed by Dr James Miller-Jones from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), have measured the distance to star system SS Cygni to be 372 light years, much closer than a previous measurement made by the Hubble Space Telescope in the 1990s.

The measurement was made possible by amateur astronomers from the American Association of Variable Star Observers (AAVSO) who alerted the team to changes in the compact star system, triggering the team to start observations with two of the world’s most accurate radio telescopes.

If you hold your finger out at arm’s length and move your head from side to side, you should see your finger appear to wobble against the background. If you move your finger closer to your head, you’ll see it starts to wobble more. We did the exact same thing with SS Cygni – we measured how far it moved against some very distant galaxies as the Earth moved around the Sun,” Dr James Miller-Jones said.

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Red Explosions Reveal Secret Life Of Binary Stars

February 6, 2013 Leave a comment

Hubble space telescope images show an expanding burst of light from a red supergiant star. Image: NASA/ESA

Hubble space telescope images show an expanding burst of light from a red supergiant star. Image: NASA/ESA

A University of Alberta professor has revealed the workings of a celestial event involving binary stars that produce an explosion so powerful its luminosity ranks close to that of a supernova, an exploding star.

Theoretical astrophysicist Natalia Ivanova says researchers have long debated about what happens when binary stars, two stars that orbit one another, come together in a “common envelope.” “When this dramatic cannibalizing event ends there are two possible outcomes: the two stars merge into a single star or an initial binary transforms into an exotic short-period one,” said Ivanova. The event is believed to take anywhere from a dozen days to a few hundred years to complete—an extremely fast time frame in terms of celestial events, Ivanova says.

More than half of all stars in the universe are binary stars, but Ivanova says it was not known what a common envelope event would look like until now.

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