Astronomers find new way to measure the pull of gravity at the surface of distant stars

January 1, 2016
How much would you weigh on another star? The timescale of turbulence and vibration at a star's surface, based on its brightness variations, tells you its surface gravity. If stars had solid surfaces on which you could stand, then your weight would change from star to star. Here we show how much a 75-kg adult would tip the bathroom scale in the surface gravities of three stars. The sun is hotter than a sauna, but don't expect to lose weight there. You'd weigh 20 times more than on Earth. A red giant star (the far-future fate of our Sun, with a diameter about 35 times larger) has a much weaker pull at its surface, so you'd be 50 times lighter. Credit: Jaymie Matthews and Thomas Kallinger

Researchers have found a new way to measure the pull of gravity at the surface of a star. For distant stars with planets orbiting them, this information is key in determining whether any of those planets can harbour life.

The new method is described in a study published today in Science Advances. The research was led by University of Vienna's Thomas Kallinger and involved UBC Professor Jaymie Matthews as well as astronomers from Germany, France and Australia.

Knowing the of a star is essentially knowing how much you would weigh on that star. If stars had solid surfaces on which you could stand, then your weight would change from star to star. The Sun is hotter than a sauna, but don't expect to lose weight there. You'd weigh 20 times more than on Earth. A red giant star (the far-future fate of our Sun) has a much weaker pull at its surface, so you'd be 50 times lighter.

The new method allows scientists to measure surface gravity with an accuracy of about four per cent, for stars too distant and too faint to apply current techniques. Since surface gravity depends on the star's mass and radius (just as your weight on Earth depends on its mass and radius), this technique will enable astronomers to better gauge the masses and sizes of distant stars. It will play an exciting role in the study of beyond the Solar System, many so distant that even the basic properties of the stars they orbit can't be measured accurately.

"If you don't know the star, you don't know the planet," said study co-author, UBC Professor Jaymie Matthews. "The size of an exoplanet is measured relative to the size of its parent star. If you find a planet around a star that you think is Sun-like but is actually a giant, you may have fooled yourself into thinking you've found a habitable Earth-sized world. Our technique can tell you how big and bright is the star, and if a planet around it is the right size and temperature to have water oceans, and maybe life."

The new technique called the autocorrelation function timescale technique, or timescale technique for short, uses subtle variations in the brightness of recorded by satellites like Canada's MOST and NASA's Kepler missions.

Future space satellites will hunt for planets in the 'Goldilocks Zones' of their stars. Not too hot, not too cold, but just right for liquid water oceans and maybe life. Future exoplanet surveys will need the best possible information about the stars they search, if they're to correctly characterize any planets they find.

"The timescale technique is a simple but powerful tool that can be applied to the data from these searches to help understand the nature of stars like our Sun and to help find other planets like our Earth," said Kallinger, the study's lead author.

Explore further: Nearby star hosts closest alien planet in the 'habitable zone'

More information: Precise stellar surface gravities from the time scales of convectively driven brightness variations, dx.doi.org/10.1126/sciadv.1500654

Related Stories

Kepler's six years in science (and counting)

May 13, 2015

NASA's Kepler spacecraft began hunting for planets outside our solar system on May 12, 2009. From the trove of data collected, we have learned that planets are common, that most sun-like stars have at least one planet and ...

Monster planet is 'dancing with the stars'

December 16, 2015

A team made up almost entirely of current and former Carnegie scientists has discovered a highly unusual planetary system comprised of a Sun-like star, a dwarf star, and an enormous planet sandwiched in between.

What kinds of stars form rocky planets?

December 3, 2015

As astronomers continue to find more and more planets around stars beyond our own Sun, they are trying to discover patterns and features that indicate what types of planets are likely to form around different kinds of stars. ...

Measuring the mass of a Mars-size exoplanet

June 18, 2015

Determining the size of an Earth-size exoplanet by the amount of starlight it blocks hundreds of light-years away once was the realm of science fiction. Measuring the mass of such a small planet based on its gravity was ...

Recommended for you

Hubble catches a transformation in the Virgo constellation

December 9, 2016

The constellation of Virgo (The Virgin) is especially rich in galaxies, due in part to the presence of a massive and gravitationally-bound collection of over 1300 galaxies called the Virgo Cluster. One particular member of ...

Scientists sweep stodgy stature from Saturn's C ring

December 9, 2016

As a cosmic dust magnet, Saturn's C ring gives away its youth. Once thought formed in an older, primordial era, the ring may be but a mere babe – less than 100 million years old, according to Cornell-led astronomers in ...

Khatyrka meteorite found to have third quasicrystal

December 9, 2016

(Phys.org)—A small team of researchers from the U.S. and Italy has found evidence of a naturally formed quasicrystal in a sample obtained from the Khatyrka meteorite. In their paper published in the journal Scientific Reports, ...

31 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Protoplasmix
5 / 5 (9) Jan 01, 2016
More information: Precise stellar surface gravities from the time scales of convectively driven brightness variations, dx.doi.org/10.1126/sciadv.1500654
Link error, "DOI Not Found" (incorrect or might not be active yet)

I think this is the Science Advances article here: http://advances.s...abstract
wduckss
3.2 / 5 (13) Jan 02, 2016
"Since surface gravity depends on the star's mass and radius"
Incorrect and poor reproduction of my text (The causal relation between a star and its temperature, gravity, radius and color http://www.svemir...l#ring).

The surface gravity is directly related to the rotation of the stars around its axis, slower rotation lower surface gravity, faster = higher surface gravity.

The mass red star small, medium and very large mass gives a similar surface gravity ... etc.
Whydening Gyre
5 / 5 (9) Jan 02, 2016
"Since surface gravity depends on the star's mass and radius"
Incorrect and poor reproduction of my text (The causal relation between a star and its temperature, gravity, radius and color http://www.svemir...l#ring).

The surface gravity is directly related to the rotation of the stars around its axis, slower rotation lower surface gravity, faster = higher surface gravity.

The mass red star small, medium and very large mass gives a similar surface gravity ... etc.

So.... you're saying it's all - relative?
Mike_Massen
2.1 / 5 (14) Jan 02, 2016
wduckss claimed
The surface gravity is directly related to the rotation of the stars around its axis, slower rotation lower surface gravity, faster=higher surface gravity
Beg pardon ?
This appears as correlation & Not causation, I have seen your link, there's several problematic issues from language through to interpretations not consistent with cognition of variance

Eg To claim ALL galaxies really should be accelerating away & none that might collide discounts Gravitation in comparatively local regions of sufficient to pull together with the potentially large regions of variance offered by the dynamic re n-body problem.

wduckss claims
The mass red star small, medium and very large mass gives a similar surface gravity ...etc
Really ?
Where is the data supporting your claims ?

& wduckss, how do You define 'surface' of a star in first place so its relevant to point you determine gravity as its plasma ie Not a solid or liquid ?

Physics not propaganda !
wduckss
4.1 / 5 (9) Jan 02, 2016
Whydening Gyre

So.... you're saying it's all - relative?


Rotation of the star affects the radius, temperature, color, and surface gravity.
Rapidly rotating small star has a higher surface gravity of a red giant (as blue or white color and a temperature greater than the red giant).
Mass is not important in this instance, because the small stars are colors from red to white as the Giants (Sun = 1). ...
wduckss
4.1 / 5 (9) Jan 02, 2016
Mike Massen
"Really ?
Where is the data supporting your claims ?"

It is not necessary to be on the surface to achieve results (gaseous planets, sun ...).

Found for example in the table below:
Betelgeuse as opposed to R Doradus, R Doradus, Aldebaran, Arcturus, Fomalhaut b, etc.
All data in the text of have the link to the Wikipedia.

I did not understand that part of the text refers to the "... Eg claim that ALL galaxies really ..."
Mike_Massen
2 / 5 (13) Jan 03, 2016
wduckss missed the point or misread my question
It is not necessary to be on the surface to achieve results (gaseous planets, sun ...)
The point is "There is NO surface" its plasma !
ie. Look at our sun, the edge which some relate to the surface as a intensity/P distribution of light re absorption/emission, not necessary same 'surface' for assessing gravity...

To clarify issue re an 'equivalent' surface in respect of a gravitational assessment you have to decide where in the plasma/gas field the equivalent boundary point *is* IF it had a surface ?

You made the claim "The mass red star small, medium and very large mass gives a similar surface gravity" and I asked for the data (that you obviously must have read) to support that claim ?

But wduckss only offered a vague hand wave
All data in the text of have the link to the Wikipedia
Please be specific, efficient to do so, there are many, useful link please ?

My last comment was addressing variance issues
my2cts
2.5 / 5 (11) Jan 03, 2016
@MM
wduckss states that the paper is a plagiarism of a writing of his own, but that Kallinger is dyslectic. Why do you even argue with him?
Mike_Massen
1.9 / 5 (13) Jan 03, 2016
my2cts asked
@MM
wduckss states that the paper is a plagiarism of a writing of his own, but that Kallinger is dyslectic. Why do you even argue with him?
Not keen on the spread of mis-information, addressing bias, interested in convergence offer approach to dialectic, increase patience threshold and with the slim chance meandering disparate opinions out there might have some basis somewhere to approach a viable basis, hence happy to challenge in conjunction with evidence or at the very least touch on the maths and overall it might even get some to lift their game, after-all we are not mere static constructs as the dynamic re cognition has minimal chance of ever reaching an asymptote & especially so in this era as tools for understanding Physics are due for a significant advance, more later...

And I could do with some light relief from my other rather more stringent cerebral activities ;-)
Whydening Gyre
5 / 5 (7) Jan 03, 2016
And I could do with some light relief from my other rather more stringent cerebral activities ;-)

I'm curious... Please elucidate.
wduckss
4.1 / 5 (9) Jan 03, 2016
I am sorry Mike_Masse, I can not give you a hypothesis and speculation.

I offer only existing evidence lined up, from the red-cold, to white-hot stars, which can be checked.

My only one contention is that the rotation has an important role as derived from the data.

You decide to, guesswork and speculation or existing evidence.

My goal posts is a was that the authors of the article use existing checked evidence and stop incorrect speculation.
lengould100
4 / 5 (2) Jan 03, 2016
wduckss claimed "slower rotation lower surface gravity, faster = higher surface gravity." -- error -- faster rotation equals reduced gravity, all else being equal.
Nik_2213
3.7 / 5 (3) Jan 03, 2016
Brilliant work !! It's sort-of astro-seismology, and so elegant. As I understand it, the lower the 'visible surface' gravity, the slower the 'pulse'. Follow the link and grab the PDF...

IIRC, beyond the range of parallax determinations, deciding a *single* star's type is usually done with spectroscopy, as there's a different pattern of 'lines' in large and small stars of similar colour.

( Binaries & higher multiples, you can figure the masses from separation and orbital period, provided latter gives enough motion to feed the math... )

Snag, as I understand it, is 'lines' spectroscopy has all sorts of problems with flares and such. This 'pulse' approach elegantly sidesteps that...
Mike_Massen
1.4 / 5 (11) Jan 03, 2016
Whydening Gyre asked
And I could do with some light relief from my other rather more stringent cerebral activities ;-)
I'm curious... Please elucidate
Hmmm, Lottsa disparate interests; trading ~12 ASX tech stocks daily (6:30am start) writing 8051 code for wifi instrumentation products, designing circuit boards, getting to grips with Zinc/Copper combinatorial biochem re anthocyanins & addressing paradigm I offered in my paper to Curtin University that "Copper is the only mineral, we need in greater quantity than we currently consume, which we adapted to from as long as ~7000yrs ago that never arose from within food"... Eg Avg intake currently in Australia from so called 'normal' food supply is ~300mcg/day total, WHO has identified homeostasis at 100mcg/Kg of body weight per day (for me 7mg/day), our ancestors consumed ~60mg/day - all up a huge disparity... To mix things up over a beer or red whine I explore alternate refreshers in Relativity & cook...
Mike_Massen
1.9 / 5 (13) Jan 03, 2016
wduckss misread my question
I am sorry Mike_Masse, I can not give you a hypothesis and speculation
Although I offered the point Sol not having an actual (firm) surface & invited comment on how to estimate that for the point re gravity equivalent

wduckss says
I offer only existing evidence lined up, from the red-cold, to white-hot stars, which can be checked
My question was & still is Where is the data re the Evidence, you must have read it somewhere if so from what specific source please ?

wduckss says
My only one contention is that the rotation has an important role as derived from the data
This suggests correlative only, what is the causal relationship ?

wduckss says
You decide to, guesswork and speculation or existing evidence
No. Thats not how Science works, if you make a claim then offer evidence or keen maths rationalisation.

wduckss says
.. the authors of the article use existing checked evidence ..
Fine but, do you have any data ?
Mike_Massen
1.9 / 5 (13) Jan 03, 2016
lengould100 observed with a claim
wduckss claimed "slower rotation lower surface gravity, faster = higher surface gravity." -- error -- faster rotation equals reduced gravity, all else being equal
Hmmm, are you suggesting a high rotational rate will somehow offset the force of gravity, it would have to be immensely fast to make even a little effect comparatively so.

ie. Mass rotation isnt in Newtonian gravitation or even in Einsteins gravitational field equations IIRC, so only other potential 'force' to offer a vector "pulling" away from the surface would have to be centrifugal and to avoid confusion re centripetal see this link which is a fair summary:-
https://en.wikipe...al_force

Its just that wduckss offered a suggestion of causality which to me so far appears as mere correlation & with a small sample set its not likely relevant as to a useful pointer to investigate a causal relationship, so can you lengould100 clarify your view ?
bluehigh
4.1 / 5 (9) Jan 03, 2016
@WG

... and Mad Mike does all that cerebral stuff every day before lunch, then he gets real busy.
Mike_Massen
1.9 / 5 (13) Jan 04, 2016
bluehigh with nothing useful as perfectly normal for him says
@WG
... and Mad Mike does all that cerebral stuff every day before lunch, then he gets real busy
Too right, ASX closes 1-1:10pm Perth time with any remnant confirmations turning up in my inbox expected no later than ~1:35pm, now 1:17pm twiddling thumbs waiting for commsec & cmc electrons to dribble into my offsets bank balance :o), leaves me free rest of day to pin down the various plebes;
who__just___Can't__get__their___heads___around___proven___relativity__!

Ah bluehigh, have you worked a way around your oddball lower middle bogan interpretation re simultaneity in Special Relativity, want some help to orient those preoccupied neurons so you dont start barking at floating orbs. moon included, hey maybe there's room on the back of your motorbike for a NIST atomic clock, can you reach 32Km/hr on yer treddlie ?

Hows your 3min attention span, swimming ?
https://www.youtu...KqIoqSIY
bluehigh
4.1 / 5 (9) Jan 04, 2016
Well Mike, either you're smarter than the average bear or a liar. My CommSec CDIA account requires 24 hours for settlement (a legal requirement). However, I don't worry about making the tiny trading margins like you need to pay for your anti-psychotic medication. I've got plenty of cash on hand to satiate my desires. Now piss off and stop polluting these comments with your arrogant narrow minded tosh you guttersnipe.
wduckss
4.1 / 5 (9) Jan 04, 2016
wduckss claimed "slower rotation lower surface gravity, faster = higher surface gravity." -- error -- faster rotation equals reduced gravity, all else being equal.


Persistently you use the hypothesis without of insight in evidence.

Betelgeuse mass from 7.7 to 20 (Sun) rotates 5 km / sec, a surface gravity of 0.5 CGS,
Beta Pictoris mass 1.8 rotates 130 km / sec, a surface gravity of 4.15 cgs, etc.
Whydening Gyre
5 / 5 (7) Jan 04, 2016
wduckss claimed "slower rotation lower surface gravity, faster = higher surface gravity." -- error -- faster rotation equals reduced gravity, all else being equal.

Why?
Whydening Gyre
5 / 5 (7) Jan 04, 2016
Hmmm, Lottsa disparate interests; trading ~12 ASX tech stocks daily (6:30am start) writing 8051 code for wifi instrumentation products, designing circuit boards, getting to grips with Zinc/Copper combinatorial biochem re anthocyanins & addressing paradigm I offered in my paper to Curtin University that "Copper is the only mineral, we need in greater quantity than we currently consume, which we adapted to from as long as ~7000yrs ago that never arose from within food"... Eg Avg intake currently in Australia from so called 'normal' food supply is ~300mcg/day total, WHO has identified homeostasis at 100mcg/Kg of body weight per day (for me 7mg/day), our ancestors consumed ~60mg/day - all up a huge disparity... To mix things up over a beer or red whine I explore alternate refreshers in Relativity & cook...

Wow... I only trade stocks and bend silverware...
Oh - and delimit random processes in closed set events...
Mike_Massen
1 / 5 (10) Jan 04, 2016
Whydening Gyre offered
..To mix things up over a beer or red whine I explore alternate refreshers in Relativity & cook...
Wow... I only trade stocks and bend silverware...Oh - and delimit random processes in closed set events
Ah, art of metalworking, a noble way to pass the time indeed whilst endearing oneself to the fairer longer lived walking erogenous zones supplying them with suitable accoutrements they just *must have* for that special occasion to impress those of desirable chromosomes or one_up_woman_ship at the local show & tell office lunch bitch session, reminds me, bluehigh resorting to bogan net rage at flimsiest of all triggers again, talk about predictable :P

Lotto given more title than deserved ? To be in it to win it I guess or pot luck at what the wife might dish up, could apply that to shares but, regular patterns, night follows day, Details matter.

Shares: Ideal system for transferring capital from the impatient to the patient ;-)
Mike_Massen
1.4 / 5 (11) Jan 04, 2016
bluehigh found his problem
Well Mike, either you're smarter than the average bear or a liar
I don't worry one iota re comparative capacity wastes effort. Too busy finding out the "Details" ie commsecone/hotcopper nick (not cmc) - easily proved try a PM ?
More interesting to address Details in lines of research & commercial upside, been at it for ages :P

bluehigh claims
My CommSec CDIA account requires 24 hours for settlement..
Eh ? Its T+3 & changes to T+2 Mar 2016 with outside settlements account. You been forced on cash balance settle due to bad Veda ?

bluehigh claims
However, I don't worry about making the tiny trading margins like you need to pay for your anti-psychotic medication
No meds, great supps, not appropriate to state stocks, how often or margins :/

ooh bluehigh shows himself yet Again
Now piss off and stop polluting these comments with your arrogant narrow minded tosh you guttersnipe
Unlike you I provide useful info not barbs!
Mike_Massen
1.4 / 5 (11) Jan 04, 2016
wduckss claims
Persistently you use the hypothesis without of insight in evidence
No. Didn't you notice I repeatedly Asked for evidence I didnt make claims re causation I Asked You for data, which I see you have now supplied below, incorrect to claim I "use a hypothesis" I have been Asking questions

wduckss offered a little data
Betelgeuse mass from 7.7 to 20 (Sun) rotates 5 km / sec, a surface gravity of 0.5 CGS,
Beta Pictoris mass 1.8 rotates 130 km / sec, a surface gravity of 4.15 cgs, etc
Well thats a start I guess but, hat's a Very small sample set & not nearly enough to arrive at minimal correlation let alone to start & develop a causal model, your use of CGS I take it you meant "Compared to Gravity of Sol" ?

How did you determine the equivalent surface level to make that g assessment, I hope you know radius from center to determine mean surface for purpose of comparative gravity assessment doesn't have clear metric from so far away ?
antialias_physorg
5 / 5 (7) Jan 04, 2016
I think wduckss is confusing gravity with acceleration. Centrifugal force does lower the acceleration a body standing on its surface feels towards that body (most at the equator - not at all at the poles, BTW). But the GRAVITY is unaffected by the rotation. That is merely a function of mass.

it is quite possible to have a body held together by tensile strength but roatate fast enough that anything standing on its surface would be flung into space. but that does not equate to 'anti gravity'. (Note that a sun would not be held together, as it is not a solid and hence has no tensile integrity)
bluehigh
4.2 / 5 (10) Jan 04, 2016
Living is easy with eyes closed
Misunderstanding all you see
It's getting hard to be someone
But it all works out
It doesn't matter much to me.

No one I think is in my tree
I mean it must be high or low
That is you can't, you know, tune in
But it's all right
That is I think it's not too bad
wduckss
4.4 / 5 (7) Jan 04, 2016

Whydening Gyre
Why?


I did not chose his examples, take them as recommended by Wikipedia. A random selection.

Select other examples and results (if exist) remain the same as in link (up).

Instead of answering why I use: so, speak the evidence. The evidence and the legality of the front of every hypothesis and why.

The evidence supports the centrifugal forces that drives a cyclone in the center of the star (from pole to pole) and galaxies, everything else is just imagination. Slow rotation = weak cyclone and vice versa.
Mike_Massen
1.7 / 5 (11) Jan 04, 2016
wduckss claims
The evidence supports the centrifugal forces that drives a cyclone in the center of the star (from pole to pole) and galaxies, everything else is just imagination
Really where ?

How can local pressure differences, which lead to cyclones have any causal bearing on the rotation overall of the whole star, this beggars belief re the star's mass in relation to angular momentum ?

wduckss claims
Slow rotation = weak cyclone and vice versa.
Sample set way too low, so far of all the hundreds of stars studied in our own local side of our galaxy you found only 2 and both of those with problematic issues just *where* the sruface equivalent point is to assess gravity ie evidence essentially non-existent at any tangible level.

ie "Balance of Probability" doesnt assist your case, especially ignoring this
https://en.wikipe...momentum
wduckss
4 / 5 (4) Jan 05, 2016
Mike_Massen

"How can local pressure differences, which lead to cyclones have any causal bearing on the rotation overall of the whole star, this beggars belief re the star's mass in relation to angular momentum ?"

Rotation of the prevailing situation within our universe. Independent rotation of the body (gaseous planets, stars, galaxies centers) creates a cyclone at center from pole to pole (in the beginning are limited to one pole).
When Sun is visible to the poles rotate much faster than the equator (it causes change of poles). Cyclones can speed up or slow down when taking matter, because there are different speeds of rotation (stars and galaxies).
Link Cyclone instead of black holes http://www.svemir...#cykloni

my2cts
3.3 / 5 (7) Jan 05, 2016
When Sun is visible to the poles rotate much faster than the equator

This paper says that the sun rotates faster at the equator, in terms of frequency not speed:
http://www.hao.uc...ound.php

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.