Astronomy C

[Ttonyxx]

I suppose I'll post questions.

1. Name and describe two structures formed by galactic interactions.
2. Fill in the blanks: A more massive white dwarf has a _______ [larger/smaller] radius. A more massive neutron star has a _______ [larger/smaller] radius. A more massive black hole (or any other object, really) has a _______ [larger/smaller] Schwarzschild radius.
3. If the core of a massive star has a radius of 0.6 Rsun, mass of 1.5 Msun, and angular speed of 1.8*10^-7 rad/s, and collapses (with no mass or angular momentum loss) into a neutron star with radius 2.3*10^-5 Rsun, what will be the new angular speed and rotational period of the neutron star?

Click to Show Answer

1. Irregular galaxies and elliptical galaxies
2. smaller, smaller, larger
3. 

[AstroClarinet]

I suppose I'll post questions.

1. Name and describe two structures formed by galactic interactions.
2. Fill in the blanks: A more massive white dwarf has a _______ [larger/smaller] radius. A more massive neutron star has a _______ [larger/smaller] radius. A more massive black hole (or any other object, really) has a _______ [larger/smaller] Schwarzschild radius.
3. If the core of a massive star has a radius of 0.6 Rsun, mass of 1.5 Msun, and angular speed of 1.8*10^-7 rad/s, and collapses (with no mass or angular momentum loss) into a neutron star with radius 2.3*10^-5 Rsun, what will be the new angular speed and rotational period of the neutron star?

Click to Show Answer

1. Irregular galaxies and elliptical galaxies
2. smaller, smaller, larger
3. 

For 1, I meant structures within the galaxies, like rings, tidal tails, shells, warps, and starburst areas. 2 and 3 are correct; your turn!

[Ttonyxx]

Okay here we go (some questions about black holes):
1) If the sun was replaced by a black hole of mass , what would change?
2) Quick, what's the Schwarzschild radius of the above black hole in kilometers?
3) It turns out that the Schwarzchild radius can be applied to solve for other important values as well. If the sun had the same mass as the black hole above, what would the time dilation be at 100km away from the center of this new sun? Show work.
4) Bob is 75kg and is sent into space to explore this black hole. What is the tidal force he experiences if he is 2 meters tall and 1km away from the black hole? Show work.
5) What is the approximate lifetime of this black hole in years? Show work.

[AstroClarinet]

Okay here we go (some questions about black holes):
1) If the sun was replaced by a black hole of mass , what would change?
2) Quick, what's the Schwarzschild radius of the above black hole in kilometers?
3) It turns out that the Schwarzchild radius can be applied to solve for other important values as well. If the sun had the same mass as the black hole above, what would the time dilation be at 100km away from the center of this new sun? Show work.
4) Bob is 75kg and is sent into space to explore this black hole. What is the tidal force he experiences if he is 2 meters tall and 1km away from the black hole? Show work.
5) What is the approximate lifetime of this black hole in years? Show work.

Click to Show Answer

1. The solar system would remain stable, but there'd be no light from the Sun so life on Earth would die out
2. 30
3. Time will run about 0.8 times as quickly as it would far from the black hole's gravitational influence. , so 
4. 1E10 N assuming the distance to the black hole is the distance to the Schwarzschild radius, otherwise Bob would be in the black hole. 
5. 2E70 yr assuming the BH doesn't absorb any energy from the surrounding environment. 

[Ttonyxx]

Okay here we go (some questions about black holes):
1) If the sun was replaced by a black hole of mass , what would change?
2) Quick, what's the Schwarzschild radius of the above black hole in kilometers?
3) It turns out that the Schwarzchild radius can be applied to solve for other important values as well. If the sun had the same mass as the black hole above, what would the time dilation be at 100km away from the center of this new sun? Show work.
4) Bob is 75kg and is sent into space to explore this black hole. What is the tidal force he experiences if he is 2 meters tall and 1km away from the black hole? Show work.
5) What is the approximate lifetime of this black hole in years? Show work.

Click to Show Answer

1. The solar system would remain stable, but there'd be no light from the Sun so life on Earth would die out
2. 30
3. Time will run about 0.8 times as quickly as it would far from the black hole's gravitational influence. , so 
4. 1E10 N assuming the distance to the black hole is the distance to the Schwarzschild radius, otherwise Bob would be in the black hole. 
5. 2E70 yr assuming the BH doesn't absorb any energy from the surrounding environment. 

Yup! Everything looks good. Your turn.

[AstroClarinet]

An alien civilization in another galaxy lives on a rogue planet orbiting their galactic center.
1) If their planet's orbital radius is 15 kpc and is moving at 300 km/s, what is the mass of the galaxy within that radius? (in solar masses)
2) The civilization observes Earth when they is at opposite sides of their planet's orbit around their galaxy (they're very patient) and measures Earth's position in the sky to change by 8 arcmin. How far are they from Earth, in Mpc?
3) What would be the radiant flux density received by the civilization from the Sun? (in W/m²)
4) Rogue planets are detected using microlensing. Which DSO (well, a compact object in the DSO) was involved in a microlensing event used to discover a distant star, and what was this star called?

[Jehosaphat]

An alien civilization in another galaxy lives on a rogue planet orbiting their galactic center.
1) If their planet's orbital radius is 15 kpc and is moving at 300 km/s, what is the mass of the galaxy within that radius? (in solar masses)
2) The civilization observes Earth when they is at opposite sides of their planet's orbit around their galaxy (they're very patient) and measures Earth's position in the sky to change by 8 arcmin. How far are they from Earth, in Mpc?
3) What would be the radiant flux density received by the civilization from the Sun? (in W/m²)
4) Rogue planets are detected using microlensing. Which DSO (well, a compact object in the DSO) was involved in a microlensing event used to discover a distant star, and what was this star called?

If you don't mind me jumping in, I need to work on this stuff too. I'm really rough on math, but I've never been taught any of it so any help is much appreciated!

Click to Show Answer

 
1. 314,000 solar masses (I used the circular velocity formula, no clue if it is the right one)
2. 12.9 Mpc (I used the small angle formula, again, not sure if that is the right one)
3. 1.93 x 10-15 W/m2 (probably wrong as well)
4. MACS J1149.5 + 2223, the star's name is Icarus 

[AstroClarinet]

An alien civilization in another galaxy lives on a rogue planet orbiting their galactic center.
1) If their planet's orbital radius is 15 kpc and is moving at 300 km/s, what is the mass of the galaxy within that radius? (in solar masses)
2) The civilization observes Earth when they is at opposite sides of their planet's orbit around their galaxy (they're very patient) and measures Earth's position in the sky to change by 8 arcmin. How far are they from Earth, in Mpc?
3) What would be the radiant flux density received by the civilization from the Sun? (in W/m²)
4) Rogue planets are detected using microlensing. Which DSO (well, a compact object in the DSO) was involved in a microlensing event used to discover a distant star, and what was this star called?

If you don't mind me jumping in, I need to work on this stuff too. I'm really rough on math, but I've never been taught any of it so any help is much appreciated!

Click to Show Answer

 
1. 314,000 solar masses (I used the circular velocity formula, no clue if it is the right one)
2. 12.9 Mpc (I used the small angle formula, again, not sure if that is the right one)
3. 1.93 x 10-15 W/m2 (probably wrong as well)
4. MACS J1149.5 + 2223, the star's name is Icarus 

I got 3.14*10¹¹ solar masses and 1.92*10^-22 W/m² on 1 and 3, but everything else is correct! I would recommend looking back over your unit conversions (something I honestly struggle with the most too) for km, kpc, and Mpc; you're free to post your work if you're not sure where you made a mistake.

Your turn!

[Jehosaphat]

I just went back through my work and realized I forgot to account for some kiloparsecs and stuff. I fixed it and got your answers, so that's good.

Suppose we receive mysterious transmissions from deep space, and in order to decide if we should look deeper into them, we attempt to locate them. We find their source around a star, and we take a hydrogen spectra and find a line’s wavelength to be 413.3 nm, above it’s typical wavelength of 410.2 nm.

1. What is the redshift of this star?
2. In km/s, how fast is the star moving away from us?
3. How long ago was this light transmitted?
4. What is the absolute magnitude of the star, if the apparent magnitude is 28.5?
5. This star is pretty far out there, but it is nothing compared to the farthest known Type 1a Supernova. What is its name and what is its redshift?
6. To cap off all my redshift talk, what redshifts is the CANDELS survey studying?

[Ttonyxx]

I just went back through my work and realized I forgot to account for some kiloparsecs and stuff. I fixed it and got your answers, so that's good.

Suppose we receive mysterious transmissions from deep space, and in order to decide if we should look deeper into them, we attempt to locate them. We find their source around a star, and we take a hydrogen spectra and find a line’s wavelength to be 413.3 nm, above it’s typical wavelength of 410.2 nm.

1. What is the redshift of this star?
2. In km/s, how fast is the star moving away from us?
3. How long ago was this light transmitted?
4. What is the absolute magnitude of the star, if the apparent magnitude is 28.5?
5. This star is pretty far out there, but it is nothing compared to the farthest known Type 1a Supernova. What is its name and what is its redshift?
6. To cap off all my redshift talk, what redshifts is the CANDELS survey studying?

Click to Show Answer

1. 
2. 
3. 
4. 
5. SN UDS10Wil, 1.914
6. 8 to 1.5