Two-Faced Star Exposed | Hacker News Reader

Two-Faced Star Exposed

caltech.edu

46 pointsbazodedo15 comments

- "The study, titled "A rotating white dwarf shows different compositions on its opposite faces," was funded by Caltech's Walter Burke Institute for Theoretical Physics, the European Research Council, The Leverhulme Trust, and the United Kingdom's Science and Technology Facilities Council."

and is freely available to the general public here [0], under the Creative Commons license. (OP press release only linked to a paywall).

[0] https://www.researchsquare.com/article/rs-2029380/v1.pdf

> "Not all, but some white dwarfs transition from being hydrogen- to helium-dominated on their surface," Caiazzo explains. "We might have possibly caught one such white dwarf in the act."

Wicked cool! The article goes on to explain that it may be due to a difference in the strength of the magnetic fields on either side of the star...

I might be mis-remembering from astronomy class ( long ago now ) but I'd thought that these transitions usually happen very quickly -- it's interesting that we can just watch it go!

IANAastrologist, but "very quickly" probably still means several thousand years in astronomical terms.

* Astronomer.

If you were an Astrologer, it would likely lend less credence to your comment. :)

Could it be that it's not actually a white dwarf? Perhaps we're making the wrong assumption because it gives off light like a white dwarf and the surface that we see appears to be hydrogen and helium based on spectrometry.

Maybe it's a planet that had its atmosphere ignited? That way it could have a super strong magnetic (iron) core while the exterior would appear like that of a white dwarf. This would explain a magnetic field that's strong enough to keep the two elements in alignment, matching the poles.

The sci-fi fan in me wants to believe that a super advanced alien race did this on purpose so they could make a giant generator out of it. I mean, it fully rotates every 15 seconds which would be a pretty damned good alternating current if you surrounded it with a lot of ferromagnetic wire.

Another reason why one might do this on purpose is to make an "anchor" or clock of sorts that gives off easily detectable gravitational waves from a great distance. As the helium side would have more mass than the hydrogen side and thus the gravity surrounding the object would be regularly rising and falling along its rotational axis.

Should we find more astronomical objects like this in the future we should check to see if they are aligned in any way that would make it easy to navigate your way through the celestial area like an enormous set of GPS satellites.

Maybe it's a planet that had its atmosphere ignited?

Because a white dwarf is about 250,000 times as dense as a planet, with the associated higher gravity, which you can measure at distance. And the magnetic field looks to be a couple of orders of magnitude higher than you could get from a 'normal matter' iron core, no matter how fast you spin it. And the hydrogen and helium are fusing, not burning, and planets don't seem to support that (try as we might here on earth). So...pretty clear it's not a planet.

Sorry - I don't mean to shoot you down, but while your overall point is correct, those are not the reasons we know why:

1) We can only estimate gravitational fields remotely when objects are interacting, by measuring the time it takes them to orbit each other - the article specifically says that the object is "floating alone in space".

2) The paper (https://assets.researchsquare.com/files/rs-2029380/v1_covere...) discusses the possibility of a magnetic field being responsible for the two-sided effect, but doesn't mention that they specifically measured it. Apparently measurement is possible for large magnetic fields by looking for circular polarisation but I don't think they have found that in this case.

3) There is no fusion happening in a white dwarf - they glow with residual heat from the original star.

Wikipedia has a lot of detail in their article: https://en.wikipedia.org/wiki/White_dwarf

I stand corrected. I definitely missed the "floating alone in space" part...for some reason I got in my head there was a companion.

They did discuss that possibility, at least in the paper, and it was my first thought for an explanation, but I think they discounted it because it would require an unrealistic or impossible orbit.

I jumped to a similar conclusion. Not my best post.

Happens to the best of us :-)

https://xkcd.com/1053/

How can we measure the gravitational field of such a distant object?

Influence on the movement relative to closeby objects. But as astutely pointed out above, I'm wrong here because the paper thinks there's no closeby objects.

If you're willing to invoke 'alien technology' as an explanation then no-one could really argue differently because we don't know what aliens are capable of. A few things that come to mind:

a) That seems like an awful lot of trouble to go to when you could surely directly harvest the energy of a star much more easily, and use that to drive whatever machinery you wanted to build.

b) How would one ignite an atmosphere and once having done so, keep it burning? Would it not all burn up in a short time? Say a few weeks at most?

c) You can't fool a spectrum - the light coming from such an object would indicate its chemical composition; if it looks like primarily H and He then that's what it is. Planetary atmospheres tend to be low in those elements because they get blown away over time.

d) As another commenter points out, the magnetic field of a planet is tiny in comparison to that required for the effect the paper is postulating - Earth's magnetic field strength for example is less than 1 gauss, whereas the scientists here are suggesting fields of a few thousands to a million gauss. Still not that high for a stellar object, but very high for a planet.

Of course I'd love for us to find evidence of aliens - but I don't think this is it.

Unusual white dwarf star is made of hydrogen on one side and helium on the other

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