Help with Doppler shift galaxy question

In summary, the student is seeking help with a past exam question about a nearby star with a similar spectrum to the sun. The star has a periodic Doppler shift with a period of 10^6s and velocity amplitude of 90m/s. The question asks for the mass of an "invisible companion" to the star and the distance between the two as they eclipse. The student is wondering what information they can obtain using the period, velocity amplitude, and mass. They mention the possibility of using the Virial Theorem and determining the velocity of the galaxy using the semi major axis and combining it with the doppler shift information. The conversation also mentions the use of guesses for the orbit and suggests not relying on specific equations. A helpful
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Homework Statement


Hi, I'd really appreciate being pointed in the right direction with this past exam question, as I just have no idea how to approach it and can't find similar examples in my notes anywhere.
A nearby star has a spectrum similar to the sun, suggesting it has the same mass. The Doppler shift of lines in the stellar spectrum vary sinusoidally with a period of 10^6s and velocity amplitude of 90m/s

The question then asks for things like the mass of the 'invisible companion' to the star, and then lead onto finding the distance from one star to the other as they eclipse, etc.

What I'm really asking, is what information can I get using the period, velocity amplitude, and mass?

Any help appreciated!

Homework Equations


Can the Virial Theorem be used?
(1/2)I''=2U+Ω where I= Σmr^2, U is kinetic energy and Ω is potential energy.
v=(2pia)/P I could find the velocity of the galaxy if I knew the semi major axis, then maybe combine this with the doppler shift information given in the question?

The Attempt at a Solution


Some ideas above..
 
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What I'm really asking, is what information can I get using the period, velocity amplitude, and mass?
The doppler shift tells you something about the speed of the star - the fact that the doppler shift is periodic tells you the star is orbiting something.
You may need to make some guesses about the orbit - but if you know the orbit-speed and you know the orbit period, then you should be able to figure out the likely mass of the primary. How would you normally do this?

What you don't want to do is try to guess the "right" equation to use.
Note: this is not a "doppler shift galaxy" question.
 
  • #3

FAQ: Help with Doppler shift galaxy question

1. What is the Doppler shift effect?

The Doppler shift effect is the change in frequency or wavelength of a wave as it moves towards or away from an observer. This effect is commonly observed in sound waves, where a moving source will cause a change in pitch, and in light waves, where a moving object will cause a change in color.

2. How does the Doppler shift apply to galaxies?

The Doppler shift effect also applies to galaxies, as they are constantly moving and expanding within the universe. Due to the expansion of the universe, galaxies that are moving away from us will have their light shifted towards the red end of the spectrum (redshift), while galaxies moving towards us will have their light shifted towards the blue end of the spectrum (blueshift).

3. How does the Doppler shift help us measure the distance of galaxies?

By analyzing the amount of redshift or blueshift in the light from a galaxy, we can determine its velocity and therefore its distance from us. The greater the shift, the faster the galaxy is moving away or towards us, and the farther away it is.

4. What is the difference between radial and tangential Doppler shift?

Radial Doppler shift refers to the change in frequency or wavelength of a wave caused by its motion along the line of sight of an observer. This is the type of Doppler shift used to measure the distance of galaxies. Tangential Doppler shift, on the other hand, refers to the change in frequency or wavelength caused by the motion of the source perpendicular to the observer's line of sight.

5. How does the Doppler shift help us understand the expansion of the universe?

The redshift observed in the light from distant galaxies provides evidence for the expansion of the universe. The more distant a galaxy is from us, the faster it appears to be moving away, indicating that the universe is expanding at an accelerating rate.

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