Sound waves on distant star reveal sun-like cycle

I searched, but I didn't see where this has been posted

Sound waves on distant star reveal sun-like cycle

Finding could help researchers learn more about inner workings and evolution of stars

By Mike Wall
Space.com
updated 8/26/2010 6:03:31 PM ET


Astronomers studying sound waves on a distant star have discovered that it has a magnetic cycle similar to our sun's solar cycle.

The find marks the first time astronomers have detected a star's magnetic cycle using a method called stellar seismology, which monitors the vibrations inside a star. The result could help researchers learn more about the inner workings and evolution of stars, including our own sun.

More: www.msnbc.msn.com...

This is new to me. It says that they "measured the star's acoustic fluctuations, which CoRoT detected as slight variations in light intensity"

So, how do acoustic fluctuations cause variations in light intensity?

Originally posted by Pauligirl
So, how do acoustic fluctuations cause variations in light intensity?

I'll take a wild guess and say that because the surface of the star at an increasing angle from perpendicular to the observer looks darkened (limb darkening), variations in the surface produce local areas not perpendicular to the observer, thus a similar effect to limb darkening.

Could also be blue and redshift of the surface.

[edit on 8/26/2010 by EnlightenUp]

Maybe this is just semantics, but I can't see how they can detect "sound waves" on a distant star. From my understanding, sounds waves are actually a propegation of energy across a medium, not an actual medium of themselves. Given that, how can sounds waves propegate across the near vaccum of interstellar space?

Originally posted by rogerstigers
Maybe this is just semantics, but I can't see how they can detect "sound waves" on a distant star. From my understanding, sounds waves are actually a propegation of energy across a medium, not an actual medium of themselves. Given that, how can sounds waves propegate across the near vaccum of interstellar space?

Somebody asked that same question at the original article. A poster answered it:

Using the CoRoT (COnvection ROtation and planetary Transits) satellite, the astronomers measured the star's acoustic fluctuations, which CoRoT detected as slight variations in light intensity. By analyzing the vibrations, the researchers were able to map out some key details of HD49933's magnetic activity cycle.

they are recording the fluctuations in light intensity and using those measurements to create audible sound like the audio file below, except the file below is for a pulsar. all in all they are doing the same thing

nsfgov.http.internapcdn.net...

With that said, I still don't get the "how" of it.

reply to post by Pauligirl


Thanks for that. At least I am not the only one here who doesn't get it.

I think I may be able to help.

Sound--what we hear--is perception: something that only exists inside our brains. Acoustic waves--mechanical oscillations--from a vibrating object travel through the air and strike our eardrums, which vibrate in sympathy. These vibrations are converted from mechanical to electrochemical energy inside our ears and transmitted to our brains, which 'hear' them as 'sound'. 'Hearing' 'sounds' is the way we perceive mechanical vibrations in the mechanical media--air, water, bone, any solid object you put your ear to--around us.

What these guys mean by 'sound' is not something we can hear. It's just the mechanical oscillation of a physical object--vibration, like what happens when you ring a bell or hit a sheet of metal with a hammer. Only in this case the vibrating object isn't a sheet of metal or a bell: it's a star.

'Essentially, the star is ringing like a bell,' Metcalfe said in statement. 'As it moves through its starspot cycle, the tone and volume of the ringing changes in a very specific pattern, moving to higher tones with lower volume at the peak of its magnetic cycle.' OP Source

By 'volume' this Metcalfe chap just means the amplitude of oscillation of the star.

By 'tone' he means the frequency of oscillation.

If the star were floating in a mechanical medium--gas or liquid--its vibrations would travel through the medium and would be audible as sound to anyone listening.

However, the star is floating in a vacuum, so its vibrations aren't perceptible as sound. However, they can still be inferred by the different methods described in the article.

Puzzled by the audio file? Don't forget that any kind of energy can be converted to any other kind--mechanical to electrical, electrical to light and so on.

The star's mechanical vibrations show up as variations in its brightness. Here's how: the vibrations cause variations in the star's magnetic field. This in turn causes fountains of hot, bright gas to well up from its interior and subside in time to those magnetic variations. Thus, the brightness of the star increases and decreases in time to its mechanical vibrations.

All this, of course, is happening on the star itself.

Back on Earth, the observed variations in the star's brightness could be (let's say) recorded on a strip of film, which would have darker or brighter bands on it depending on the light intensity of the star at the time that particular bit of film was exposed to it. If you then developed the film, you could run it through an optical reader of the kind used in cinemas, which converts these variations in brightness into sound. You could then record the sound in any way you liked and play it back whenever you felt like it. Presto! The sound of a star!

Of course, that's a very crude way to do it. In fact, you would be able to convert the star's brightness variations more or less directly into a digital audio file and play that back--which is what I'm guessing they've done.

reply to post by Astyanax


I thought the question was more along the lines of "how are the oscillations actually read off the star itself?" and relatedly, "what makes these oscillations visible?"

Originally posted by EnlightenUp
I thought the question was more along the lines of "how are the oscillations actually read off the star itself?" and relatedly, "what makes these oscillations visible?"

Ah... no.

The questions were

How do acoustic fluctuations cause variations in light intensity?

and

How can sounds waves propegate across the near vaccum of interstellar space?

Both answered in my post above.

Your attempted answer is, by the way, iwrong.

reply to post by Astyanax

Your attempted answer is, by the way, iwrong.

iwrong?

I still read the first question much the same. I never addressed the second at all (obviously the "sound" doesn't travel through the vacuum).

I guess I somehow missed your answer about it and as a result I feel a bit foolish:

The star's mechanical vibrations show up as variations in its brightness. Here's how: the vibrations cause variations in the star's magnetic field. This in turn causes fountains of hot, bright gas to well up from its interior and subside in time to those magnetic variations. Thus, the brightness of the star increases and decreases in time to its mechanical vibrations.

This source does mention that doppler shift can be used but specifically mentions helioseismology:

What are these oscillations?
Leighton, Noyes, and Simon (1962) noticed in the spectrum of the Sun that some of the absorption lines were wiggling back and forth slightly with periods of around five minutes. Because the frequency of absorption lines can be shifted if the source is moving toward or away from the observer (the Doppler Shift effect), Leighton, Noyes, and Simon conjectured that the surface of the Sun is shaking back and forth. More careful observations revealed that while some parts of the surface of the Sun were moving towards us, other parts were moving away from us. It was as if there were waves, rising and falling on the surface of the Sun.

[edit on 8/27/2010 by EnlightenUp]

iwrong?

Internet wrong. Virtually wrong, not absolutely wrong.

Either that, or itypo.

Originally posted by Astyanax
The star's mechanical vibrations show up as variations in its brightness. Here's how: the vibrations cause variations in the star's magnetic field. This in turn causes fountains of hot, bright gas to well up from its interior and subside in time to those magnetic variations. Thus, the brightness of the star increases and decreases in time to its mechanical vibrations.

Ah ha! Now I get it. Thanks for putting it in a way I can understand.

And "Internet wrong. Virtually wrong, not absolutely wrong."
I'll have to remember that for future use.

Originally posted by Astyanax
Internet wrong. Virtually wrong, not absolutely wrong.

Either that, or itypo.

Had a feeling but I'm guessing initially the latter with a good save.com.

Thanks. I'll have to follow up on the details of exactly why that magnetic distortion has the effect it does as it's quite curious.