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alpacas wrote:

maybe (Click to Show Hidden Text)

1.1x10^7 m/s away from "Larcie"

bbgun34 wrote:

What I got.. (Click to Show Hidden Text)

Well yeah, disregarding radius, but I'm getting 1.79x10^15 kg/m^3.

Anyone else have any ideas?

But in the meantime maybe I'll post a more mellow problem:

A huge 4000-Kelvin tomato behaves like a blackbody. If Larcie Curbh, the astronomer observing this cosmic tomato, gets sick if she sees anything with a wavelength of at most 7000 Angstroms, what must the radial velocity of this tomato be (and in which direction) so that Larcie gets sick?

I got that the Tomato must be traveling about 10137.9 km/s away from Larcie.
How i go this answer was first getting the emitted peak wavelength of the tomato. I used Wien's law, where [u]peak wavelength=2,898,000/T[/u], where T is temperature.
Peak WL= 2,898,000/4000=[b]724.5 nm[/b]
We convert this to angstroms by multiplying by 10. We then get 7245 angstroms.
We now know that the tomato must be moving away fast enough so that its wavelength gets blueshifted 245 angstroms (I assumed that Larcie gets sick with higher wavelengths, I was confused by the wording.)
We then plug this into the redshift equation, where [u](Obs WL/Emitted WL)-1=Redshift(Z)[/u]
(7000/7245)-1=-.0338164251
We get the velocity in km/s by multiplying the redshift by the speed of light
-.338164251(299 792.458)=-10137.90921 km/s
In the end, we discover that Larcie will be sick if the tomato recedes at 10137.90921 km/s

imafish wrote:

alpacas wrote:

maybe (Click to Show Hidden Text)

1.1x10^7 m/s away from "Larcie"

Gah, I feel like such a newbie (cuz I am...)
From the 4000K tomato I looked at the blackbody curves the wavelength is .89um = 8900A.
Shift equation: Z=(change in wavelength)/(unshifted wavelength)=(7000-8900)/8900= -0.213
Velocity = Zc = (-0.213)(3.00E8) = -6.40E7 m/s

How did you get your answer?

syo_astro wrote:So what's going on with this?

foreverphysics wrote:

I don't know if this is what you are looking for, but... (Click to Show Hidden Text)

It is a fairly massive white dwarf in a binary star system. The other star is a mid-size star about the size of our sun.