Gaia satellite and amateur astronomers spot one in a billion star

July 16, 2015
Artist's impression of Gaia14aae. Credit: Marisa Grove/Institute of Astronomy

An international team of researchers, with the assistance of amateur astronomers, have discovered a unique binary star system: the first known such system where one star completely eclipses the other. It is a type of two-star system known as a Cataclysmic Variable, where one super dense white dwarf star is stealing gas from its companion star, effectively 'cannibalising' it.

The system could also be an important laboratory for studying ultra-bright supernova explosions, which are a vital tool for measuring the expansion of the Universe. Details of the new research will be published in the journal Monthly Notices of the Royal Astronomical Society.

The system, named Gaia14aae, is located about 730 light years away in the Draco constellation. It was discovered by the European Space Agency's Gaia satellite in August 2014 when it suddenly became five times brighter over the course of a single day.

Astronomers led by the University of Cambridge analysed the information from Gaia and determined that the sudden outburst was due to the fact that the white dwarf - which is so dense that a teaspoonful of material from it would weigh as much as an elephant - is devouring its larger companion.

Additional observations of the system made by the Center for Backyard Astrophysics (CBA), a collaboration of amateur and professional astronomers, found that the system is a rare eclipsing binary, where one star passes directly in front of the other, completely blocking it out when viewed from Earth. The two stars are tightly orbiting each other, so a total eclipse occurs roughly every 50 minutes.

"It's rare to see a binary system so well-aligned" said Dr Heather Campbell of Cambridge's Institute of Astronomy, who led the follow-up campaign for Gaia14aae. "Because of this, we can measure the system with great precision in order to figure out what these systems are made of and how they evolved. It's a fascinating system - there's a lot to be learned from it."

Using spectroscopy from the William Herschel Telescope in the Canary Islands, Campbell and her colleagues found that Gaia14aae contains large amounts of helium, but no hydrogen, which is highly unusual as hydrogen is the most common element in the Universe. The lack of hydrogen allowed them to classify Gaia14aae as a very rare type of system known as an AM Canum Venaticorum (AM CVn), a type of Cataclysmic Variable system where both stars have lost all of their hydrogen. This is the first known AM CVn system where one star totally eclipses the other.

"It's really cool that the first time that one of these systems was discovered to have one star completely eclipsing the other, that it was who made the discovery and alerted us," said Campbell. "This really highlights the vital contribution that amateur astronomers make to cutting edge scientific research."

AM CVn systems consist of a small and hot which is devouring its larger companion. The gravitational effects from the hot and superdense white dwarf are so strong that it has forced the to swell up like a massive balloon and move towards it.

The companion star is about 125 times the volume of our sun, and towers over the tiny white dwarf, which is about the size of the Earth - this is similar to comparing a hot air balloon and a marble. However, the companion star is lightweight, weighing in at only one percent of the white dwarf's mass.

AM CVn systems are prized by astronomers, as they could hold the key to one of the greatest mysteries in modern astrophysics: what causes Ia supernova explosions? This type of supernova, which occurs in binary systems, is important in astrophysics as their extreme brightness makes them an important tool to measure the expansion of the Universe.

In the case of Gaia14aae, it's not known whether the two stars will collide and cause a supernova explosion, or whether the white dwarf will completely devour its companion first.

"Every now and then, these sorts of binary systems may explode as supernovae, so studying Gaia14aae helps us understand the brightest explosions in the Universe," said Dr Morgan Fraser of the Institute of Astronomy.

"This is an exquisite system: a very rare type of binary system in which the component stars complete orbits faster than the minute hand of a clock, oriented so that one eclipses the other," said Professor Tom Marsh of the University of Warwick. "We will be able to measure their sizes and masses to a higher accuracy than any similar system; it whets the appetite for the many new discoveries I expect from the Gaia satellite."

"This is an awesome first catch for Gaia, but we want it to be the first of many," said the Institute of Astronomy's Dr Simon Hodgkin, who is leading the search for more transients in Gaia data. "Gaia has already found hundreds of transients in its first few months of operation, and we know there are many more out there for us to find."

Gaia's mission, funded by the European Space Agency and involving scientists from across Europe, is to make the largest, most precise, three-dimensional map of the Milky Way ever attempted. During its five-year mission, which began in late 2013, Gaia's billion-pixel camera will detect and very accurately measure the motion of stars in their orbit around the centre of the galaxy. It will observe each of the billion stars about a hundred times, helping us to understand the origin and evolution of the Milky Way.

The follow-up campaign used several professional telescopes, including those located in the Canary Islands, where observing time was made available through the International Time Program.

Explore further: Binary white dwarf stars

More information: Campbell, HC et al, Total eclipse of the heart: The AM CVn Gaia14aae / ASSASN-14cn, Monthly Notices of the Royal Astronomical Society (2015). DOI: 10.1093/mnras/stv1224

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nicholasdc
1 / 5 (4) Jul 16, 2015
A neutron star is so dense that one teaspoon (5 milliliters) of its material would have a mass over 5.5×1012 kg (that is 1100 tonnes per 1 nanolitre), about 900 times the mass of the Great Pyramid of Giza.

A teeny wad more than a simple elephant!
TechnoCreed
5 / 5 (12) Jul 16, 2015
A neutron star is so dense that one teaspoon (5 milliliters) of its material would have a mass over 5.5×1012 kg (that is 1100 tonnes per 1 nanolitre), about 900 times the mass of the Great Pyramid of Giza.

A teeny wad more than a simple elephant!

The article talks about a white dwarf not a neutron star http://chandra.ha...node/182
Returners
4 / 5 (5) Jul 16, 2015
White Dwarf =/= Neutron Star
stanlwong
5 / 5 (5) Jul 16, 2015
??

If the companion star is indeed only 1% of the white dwarf's mass as stated in the article, I would think it should not be considered a star at all.

Since the white dwarf's can only be ~1.4 solar mass (max), 1% of this is only .014 Sol, which is ~1/6 of the minimum mass for the lightest possible red dwarf star (.080 Sol).

Had the white dwarf already cannibalized so much mass from the red dwarf to reduce its mass down this low?

Or maybe this started as a sun like primary with a brown dwarf in close orbit, when the primary became a red giant, the brown dwarf cannibalized a % of the primary's expanded envelope, and the drag caused the binary to spiral closer, after the primary became a white dwarf, the close orbit caused the brown dwarf's atmosphere to swell up due to combined radiative & tidal heating, which is what we're seeing today.

Not sure the math would work if the secondary started off with the mass of an red dwarf.
McSteel
4.3 / 5 (3) Jul 16, 2015
I think they might have actually meant the companion star has only a 1% _density_ of the white dwarf. Indeed, for an Earth-sized object, the Chandra limit is between 1.4 and 1.7 Sol, IIRC...
Enthusiastic Fool
5 / 5 (10) Jul 16, 2015
According to the abstract:
"the contact phases of the WD lead to lower limits of 0.78 and 0.015 M⊙ on the masses of the accretor and donor, respectively, and a lower limit on the mass ratio of 0.019."

Looks like study constrained the donor to a minimum 1.9% of the mass of the WD.

Also in the abstract it says of the spectra:
"...hot, hydrogen-deficient spectrum with clear double-peaked emission lines, consistent with an accreting double-degenerate classification."

So the puffier donor star is also degenerate(a white dwarf)?
According to Wikipedia: https://en.wikipe...rum_star
"The ultra-short orbital periods of 10–65 minutes indicate that both the donor star and accretor star are degenerate or semi-degenerate objects."

Pretty cool that the predicted properties based on orbital period in theory match this system and are corroborated spectrally.

Wouldn't it be cool to witness a Super Chandrasekhar merger
(cont.)
Enthusiastic Fool
4.6 / 5 (5) Jul 16, 2015
(cont)
Wouldnt it be cool to witness a double degenerate Type 1a SN?

The article up top says:
it's not known whether the two stars will collide and cause a supernova explosion, or whether the white dwarf will completely devour its companion first.


Is it possible the the more massive body could reach thermonuclear criticality/SN before they merge or it devours the companion donor? Is this scenario excluded b/c it's precluded by the mass of both bodies and that it would take a Super Chandra merger to trigger a 1aSN?
Enthusiastic Fool
5 / 5 (7) Jul 17, 2015
I should temper my enthusiasm for a super Chandrasekhar merger. If the stars are close to the minimum constrained masses they would not combine to be 1.38 solar masses but something closer to .8 solar masses. :/

Sorry for the spam.
Enthusiastic Fool
4.7 / 5 (9) Jul 17, 2015
It is very difficult and even impossible to understand the structure and the processes that are going inside the stars. We have theories, but the problem is that we can check them out by direct observations and experiments. We have only pоssibility to speculate and to think that we have knowledge without objective reasons for this. Some people are very proud of our scientific "achievements" when it is doubtful whether this are achievements or deep delusion.


Yeah, there's no way we could directly observe the Sun...There's definitely delusion in some people.
mytwocts
4.6 / 5 (9) Jul 17, 2015
It is very difficult and even impossible to understand the structure and the processes that are going inside the stars. We have theories, but the problem is that we can check them out by direct observations and experiments. We have only pоssibility to speculate and to think that we have knowledge without objective reasons for this. Some people are very proud of our scientific "achievements" when it is doubtful whether this are achievements or deep delusion.

You want people to question very well established physics, while at the same time spreading religious fairy tales.
antialias_physorg
4.6 / 5 (9) Jul 17, 2015
It is very difficult and even impossible to understand the structure and the processes that are going inside the stars.

Strangley we have any number of methods of checking what goes on inside stuff.
Here on Earth we can look inside objects by CT, MR, ultrasound, seismology, PET, SPECT, and nay number of other methods.
Some of these are applicable for looking into stars (e.g. seismology, because we can observe surface waves on stars).

Then we have an entire night sky with uncountable billions of stars in various stages of their life cycle for comparison.

Don't underestimate the ingenuity of scientists when it comes to gleaning information from anything and everything.

We have only pоssibility to speculate and to think that we have knowledge without objective reasons for this.

The objective reason is prediction and test. After you make a model you test it. If it works in all cases then you have a good model.
Returners
1.8 / 5 (6) Jul 17, 2015
The model used for the Sun says the inner temperature of the Core is 17 million Kelvin. This is hot enough to power the CNO cycle, yet astrophysicists deny the Sun is burning a significant amount of the CNO cycle.

That's a perfect example of not knowing what's really going on inside of a "Star".

As for the object in question, if it accretes the matter slowly then it is not going to SN, because it's nowhere near the needed mass.
bschott
3 / 5 (2) Jul 17, 2015
You want people to question very well established physics, while at the same time spreading religious fairy tales.


Are you saying well established physics validate the current solar model and can explain all the observed solar phenomena? I hope not....

His post mentioned nothing of religion.
mytwocts
4.6 / 5 (11) Jul 17, 2015
You want people to question very well established physics, while at the same time spreading religious fairy tales.


Are you saying well established physics validate the current solar model and can explain all the observed solar phenomena? I hope not....

Are you claiming that the current solar model fails? I hope you can back them up.


His post mentioned nothing of religion.

You must be new here.
swordsman
1.2 / 5 (5) Jul 18, 2015
Far remote observations generally lead to conclusions that are incomplete, erroneous, or wrong. It is because of the lack of completeness that lead many to this endeavor.
Enthusiastic Fool
4 / 5 (4) Jul 18, 2015
Far remote observations generally lead to conclusions that are incomplete, erroneous, or wrong. It is because of the lack of completeness that lead many to this endeavor.


Handwaving from incredulity? Suit yourself.
bschott
1 / 5 (2) Jul 21, 2015
Are you claiming that the current solar model fails? I hope you can back them up."


Coronal heating, 22 year solar cycle, magnetic pole reversal, different convection models, magnetic field origins. Rings like a bell every 5 minutes, ulysses probe temperature data....

"Well established physics" has yet to offer up answers as to how these phenomena fit into their version of the solar model.

I hope you can back them up.


it's a start....

You must be new here.


That clarifies nothing WRT the "spreading of religious fairy tales".

barakn
3.9 / 5 (7) Jul 22, 2015
The model used for the Sun says the inner temperature of the Core is 17 million Kelvin. This is hot enough to power the CNO cycle, yet astrophysicists deny the Sun is burning a significant amount of the CNO cycle.

That's a perfect example of not knowing what's really going on inside of a "Star". -Returners

Neutrino studies suggest core temperature is only 15.7 million K and modern solar models use this information, so you've already set up a strawman argument. You are ignoring the fact that pp reactions can occur at lower temperatures and therefore can occur in a larger volume of the sun than can CNO cycle reactions. You have also ignored the fact that the reaction rates are dependent on the reactant concentrations and not just temperature - current estimates suggest the sun is comprised of only half a percent nitrogen.

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