Pulsating star mystery solved

November 24, 2010
This artist's impression shows the double star OGLE-LMC-CEP0227 in our neighboring galaxy the Large Magellanic Cloud. The smaller of the two stars is a pulsating Cepheid variable and the orientation of the system is such that the stars eclipse each other during their orbits. Studies of this very rare system have allowed astronomers to measure the Cepheid mass with unprecedented accuracy. Credit: ESO

(PhysOrg.com) -- By discovering the first double star where a pulsating Cepheid variable and another star pass in front of one another, an international team of astronomers has solved a decades-old mystery. The rare alignment of the orbits of the two stars in the double star system has allowed a measurement of the Cepheid mass with unprecedented accuracy. The new result shows that the prediction from stellar pulsation theory is spot on, while the prediction from stellar evolution theory is at odds with the new observations.

The new results, from a team led by Grzegorz Pietrzynski (Universidad de Concepción, Chile, Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Poland), appear in the 25 November 2010 edition of the journal Nature.

Grzegorz Pietrzynski introduces this remarkable result: "By using the HARPS instrument on the 3.6-metre telescope at ESO's La Silla Observatory in Chile, along with other telescopes, we have measured the mass of a Cepheid with an accuracy far greater than any earlier estimates. This new result allows us to immediately see which of the two competing theories predicting the masses of Cepheids is correct."

Classical Cepheid Variables, usually called just Cepheids, are unstable stars that are larger and much brighter than the Sun. They expand and contract in a regular way, taking anything from a few days to months to complete the cycle. The time taken to brighten and grow fainter again is longer for stars that are more luminous and shorter for the dimmer ones. This remarkably precise relationship makes the study of Cepheids one of the most effective ways to measure the distances to nearby galaxies and from there to map out the scale of the whole Universe.

Unfortunately, despite their importance, Cepheids are not fully understood. Predictions of their masses derived from the theory of pulsating stars are 20󈞊% less than predictions from the theory of the evolution of stars. This embarrassing discrepancy has been known since the 1960s.

To resolve this mystery, astronomers needed to find a double star containing a Cepheid where the orbit happened to be seen edge-on from Earth. In these cases, known as eclipsing binaries, the brightness of the two stars dims as one component passes in front of the other, and again when it passes behind the other star. In such pairs can determine the masses of the stars to high accuracy. Unfortunately neither Cepheids nor eclipsing binaries are common, so the chance of finding such an unusual pair seemed very low. None are known in the Milky Way.

This wide field view of part of our neighbouring galaxy, the Large Magellanic Cloud, was created from photographs taken in red and blue light as part of the Digitized Sky Survey 2. The remarkable double star OGLE-LMC-CEP0227 lies at the centre of the picture, just one of huge numbers of faint stars. Studies of this very rare system have allowed astronomers to measure mass of a Cepheid variable star with unprecedented accuracy. The field of view is approximately 2.8 degrees across. Credit: ESO

Wolfgang Gieren, another member of the team, takes up the story: "Very recently we actually found the double star system we had hoped for among the stars of the Large Magellanic Cloud. It contains a Cepheid variable star pulsating every 3.8 days. The other star is slightly bigger and cooler, and the two stars orbit each other in 310 days. The true binary nature of the object was immediately confirmed when we observed it with the HARPS spectrograph on La Silla."

The observers carefully measured the brightness variations of this rare object, known as OGLE-LMC-CEP0227, as the two stars orbited and passed in front of one another. They also used HARPS and other spectrographs to measure the motions of the stars towards and away from the Earth — both the orbital motion of both stars and the in-and-out motion of the surface of the Cepheid as it swelled and contracted.

This very complete and detailed data allowed the observers to determine the orbital motion, sizes and masses of the two stars with very high accuracy — far surpassing what had been done before for a Cepheid. The mass of the Cepheid is now known to about 1% and agrees exactly with predictions from the theory of stellar pulsation. However, the larger mass predicted by stellar evolution theory was shown to be significantly in error.

The much-improved mass estimate is only one outcome of this work, and the team hopes to find other examples of these remarkably useful pairs of to exploit the method further. They also believe that from such binary systems they will eventually be able to pin down the distance to the Large Magellanic Cloud to 1%, which would mean an extremely important improvement of the cosmic distance scale.

Explore further: Moving Closer to the Grand Spiral

More information: This research was presented in a paper to appear in the journal Nature on 25 November 2010.

Related Stories

Moving Closer to the Grand Spiral

August 1, 2005

An international team of astronomers from Chile, Europe and North America is announcing the most accurate distance yet measured to a galaxy beyond our Milky Way's close neighbours. The distance was determined using the brightness ...

The Cosmic Distance Scale

January 29, 2010

(PhysOrg.com) -- In 1908, Harvard astronomer Henrietta Swan Leavitt discovered that a class of stars called Cepheids have brightnesses that vary regularly with periods that are directly related to their intrinsic luminosities.

The Polaris Cluster

May 28, 2010

(PhysOrg.com) -- A Cepheid star is one whose mass and age results in physical conditions that generate periodic oscillations in its photosphere. A Cepheid thus varies regularly in brightness, with a period proportional to ...

Cepheids and their 'cocoons'

February 28, 2006

Using ESO's Very Large Telescope Interferometer (VLTI) at Cerro Paranal, Chile, and the CHARA Interferometer at Mount Wilson, California, a team of French and North American astronomers has discovered envelopes around three ...

There's More to the North Star Than Meets the Eye

January 9, 2006

We tend to think of the North Star, Polaris, as a steady, solitary point of light that guided sailors in ages past. But there is more to the North Star than meets the eye - two faint stellar companions. The North Star is ...

Recommended for you

Fast radio bursts may be firing off every second

September 21, 2017

When fast radio bursts, or FRBs, were first detected in 2001, astronomers had never seen anything like them before. Since then, astronomers have found a couple of dozen FRBs, but they still don't know what causes these rapid ...

Hubble discovers a unique type of object in the Solar System

September 20, 2017

With the help of the NASA/ESA Hubble Space Telescope, a German-led group of astronomers have observed the intriguing characteristics of an unusual type of object in the asteroid belt between Mars and Jupiter: two asteroids ...

Ageing star blows off smoky bubble

September 20, 2017

Astronomers have used ALMA to capture a strikingly beautiful view of a delicate bubble of expelled material around the exotic red star U Antliae. These observations will help astronomers to better understand how stars evolve ...


Adjust slider to filter visible comments by rank

Display comments: newest first

1.5 / 5 (8) Nov 24, 2010
Intriguing story: "The new result shows that the prediction from stellar pulsation theory is spot on, while the prediction from stellar evolution theory is at odds with the new observations."

Did they discover that other stars also recycle, as the Sun did 5 Gyr ago when it gave birth to the solar system?

With kind regards,
Oliver K. Manuel
4.3 / 5 (6) Nov 25, 2010
"The new result shows that the prediction from stellar pulsation theory is spot on, while the prediction from stellar evolution theory is at odds with the new observations."

Perhaps it should be noted that stellar pulsation theory AND stellar evolution theory are at odds with neutron repulsion theory AND the notion of neutron stars residing in the nucleus of all stars. In addition, if suitable quantitative models of the structure of stars powered by neutron repulsion existed, they would likely be at odds with these new observations as well.
1 / 5 (4) Nov 25, 2010
Galactic Bubbles, Exploding Stars & Solar Bubble of SW Hydrogen

These observations arise from neutron repulsion:

See: "Milky Way Bubbles Discovered by Gamma Ray Telescope"

1. Doug Finkbeiner (Harvard-Smithsonian Center for Astrophysics):

“What we see are two gamma-ray-emitting bubbles that extend 25,000 light-years north and south of the galactic center”

"We don’t fully understand their nature or origin.”

2. David Spergel (Princeton University):

“Whatever the energy source behind these huge bubbles may be, it is connected to many deep questions in astrophysics.”

With kind regards,
Oliver K. Manuel
Former NASA Principal
Investigator for Apollo
5 / 5 (4) Nov 25, 2010

My apologies. I was unaware of paper(s) that describe these Fermi gamma-ray observations that directly invoke neutron repulsion(by name) as the energy source powering these bubbles. In which publication may I find a paper that makes that claim(specific to these Fermi observations)? I'm sure Finkbeiner and Spergel would be interested.

I dunno. Seems a little silly to present those quotes as evidence of NR. May as well invoke plasma cosmology (it's already been done, really!), AWT(it's probably been done!), unicorns or pixie dust. :^)
1 / 5 (3) Nov 25, 2010
That's okay, yyz, we do not yet have a paper published that says "these Fermi gamma-ray observations" are directly caused by "neutron repulsion (by name)."

A paper published four years ago states: "Repulsive interactions between neutrons in compact stellar cores cause luminosity and a steady outflow of hydrogen from stellar surfaces. Neutron repulsion in more massive compact objects made by gravitational collapse produces violent, energetic, cosmological events (quasars, gamma ray bursts, and active galactic centers) that had been attributed to black holes before neutron repulsion was recognized." ["On the cosmic nuclear cycle and the similarity of nuclei and stars", Journal of Fusion Energy 25 (2006) 107-114].

This video also explains the role of neutron repulsion in releasing energy from the cores of heavy nuclei, stars, and galaxies.


With kind regards,
Oliver K. Manuel
Former NASA Principal
Investigator for Apollo

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.