SS Cygni is a special kind of binary system, consisting of a red dwarf star and a white dwarf. According to theoretical models, the white dwarf strips gas from its companion, which leads to periodic outbursts of intense light: a recurrent nova. However, previous observations of the system placed it too far away for those models to work, casting doubt on the theory — a problem for types of systems other than recurrent novas. A new observation using radio telescopes found a much more amenable distance, but led to another problem: why were these two distance measurements so different?

Both used a method known as parallax, a geometrical technique for measuring distances to objects relatively close to the Solar System. The key difference is how the two measurements were calibrated. Parallax doesn’t require knowledge about the emission of light from the object (unlike other distance measurements such as those that use type Ia supernovas), but it still requires reference points. [Read more…]

New distance measurements solve one mystery – and create a new one

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General relativity holds up under extreme gravity test

The general theory of relativity is the reigning champion of gravitational theories: it’s withstood tests in the Solar System, near black holes, and in binary systems. Most recently, astronomers performed detailed observations of a pulsar-white dwarf binary system, which provided an exquisite example of general relativity in action. Pulsars and white dwarfs are both the remnants of stars, but pulsars in particular are interesting: they pack the mass of a star into a sphere about 20 kilometers across. That means the gravity at the surface of a pulsar is extreme, so when one is in a binary system, it provides a laboratory for measuring strong gravitational effects.

The pulsar itself was interesting because of its relatively high mass: about 2.0 times that of the Sun (most observed pulsars are about 1.4 times more massive). Unlike more mundane objects, pulsar size doesn’t grow with mass; according to some models, a higher mass pulsar may actually be smaller than one with lower mass. As a result, the gravity at the surface of PSR J0348+0432 is far more intense than at a lower-mass counterpart, providing a laboratory for testing general relativity (GR). The gravitational intensity near PSR J0348+0432 is about twice that of other pulsars in binary systems, creating a more extreme environment than previously measured. [Read more…]

Also, let the record show: it’s possible to write an article about testing general relativity without mentioning Einstein, much less making the story about “proving him right” (or wrong).

Cosmology—the study of the Universe as a whole—requires accurate measurements of the distances to galaxies and other objects billions of light-years away. However, the reliability of those estimates depends on how accurately we know the distance to closer objects, such as the Milky Way’s satellite galaxy known as the Large Magellanic Cloud (LMC). A new study has obtained the most accurate distance to the LMC yet, which in turn leads to better cosmological measurements. The key to the new distance measure: binary systems in the LMC consisting of two aging stars in relatively large orbits.

The researchers used data from the Optical Gravitational Lensing Experiment (yes, it’s nicknamed OGLE), which was designed to look for fluctuations in dark matter density by observing stars in the LMC. While OGLE hasn’t succeeded in its primary goal of spotting clumps of dark matter, it has amassed a lot of data from 35 million stars, going back as far as 1992.

From those 35 million stars, the astronomers identified 12 eclipsing binary stars; of those, they analyzed data from eight pairs for a period of eight years. These pairs they chose are rare, consisting of stars in the helium-burning stage, which occurs after they have exhausted their core’s hydrogen fuel. Aging stars of this type have well-known intrinsic brightness in relation to their color. [Read more…]

Aging binaries provide new calibration for cosmic distances

V838 Monocerotis

A mystery: an unknown star, too faint to notice, suddenly expanded to a huge size, increasing in brightness to become one of the most luminous stars known. This star doesn’t even have a real name, just a “license plate” catalog number: V838 Monocerotis, indicating that it’s a not very important star in the constellation the Unicorn (Monoceros). However, a new paper has proposed the powerful flare could be explained by a well-accepted theory of binary star behavior, in which one star strips enough matter off the other until it suddenly grows to a huge size. These common envelope events (as they are known) could  explain the V838 Monocerotis outburst, along with some other currently mysterious flares.

A new Science paper proposes that a class of violent astronomical events that we’ve observed may be due to common envelope stars, providing more direct evidence for their existence. These cataclysms are known as “red transient outbursts,” and in brightness terms, they’re somewhere between novas (flares of nuclear activity at the surfaces of white dwarfs) and supernovas, the violent deaths of stars. N. Ivanova, S. Justham, J. L. Avendado Nandez, and J. C. Lombardi Jr. identified a possible physical model for these outbursts, based on the recombination of electrons and ions in the plasma when the stars’ envelopes merge. [Read more…]

Cannibal binary star could explain mysterious nova-like outbursts

How quickly things can change in science: just a few years ago, we were barely able to talk about the diversity of planetary systems. Now, we are able to distinguish between planets orbiting in tight binary systems from those in wide binaries. Additionally, exoplanets in tight binaries can orbit either both stars together (circumbinary, or Tatooine-like systems) or one of two stars, where the second might be like a Jupiter in the system. In wide binaries, the second star is so far away that it’s barely attached to the system, but a new set of simulations may show that may actually lead to greater instability than experienced by planets in tight binaries.

Nathan A. Kaib, Sean N. Raymond, and Martin Duncan ran extensive computer simulations to model exoplanets residing in wide binary systems. They found that perturbations from other stars outside the binary system had a profound effect on the shape of the system’s orbits. In some cases, planets were ejected from the system entirely or ended up in larger or highly eccentric (elongated) orbits. Based on these results, the researchers argued that some of the observed exoplanet systems with eccentric orbits may actually reside in wide binary systems where we haven’t yet detected the companion stars. [Read more, and watch the video!]

Bad news for some planets in binary star systems?