Question

The recently launched Hložek Space Telescope (HST) has just completed its first survey, studyingthousands of stars spread out throughout the Milky Way. Data for one of the stars in the survey, ID200, has been given to you for analysis. Given everything you learned in AST 201 this year, please answer the following questions:

a) The first set of data you receive is a spectrum of a main sequence star taken with the Mac-Donald Spectrometer onboard HST. Based on the fact that the star’s spectrum has strongHydrgen absorption lines and no molecular absorption lines, what spectral type do you be-lieve this star to be? Explain. [3 marks]

b) Based on this star’s spectral type, explain the evolutionary stages that it will go through afterit completes the main sequence phase of its life. How will this star’s life end? [3 marks]

c) HST is also equipped with the Williams Planetary Camera, which searches for planets aroundstars as their spectrum is being measured. Around this particular star, the camera detectedthree planets orbiting 5.2, 7.6, and 9.4 AU from the star. Their orbital periods are calculatedto be 2.8, 3.4, and 3.8 years respectively. Are these measurements qualitatively consistentwith the general trend predicted by Kepler’s Laws? Why or why not? [2 marks]

d) Thanks to the Webb Photometric and Astrometric Instrument also onboard HST, we are ableto determine that the star is 1.7 kpc from the centre of the Milky Way and travelling with anorbital speed of 120.0 km/s. Your classmates found other stars in the Milky Way that are 7.9and 13.7 kpc from the Galactic centre travelling with orbital speeds of 219.4 and 220.0 km/srespectively. Are these measurements consistent with the Milky Way having a significantdark matter component? Why or why not? [2 marks

Answer 1

(A)-

Starts with are in spectral type A does not contain any molecular line and has the strongest hydrogen absorption lines. because of their temperature most of the hydrogen atoms exist in their excited state so the observed star is of spectral type A.

(B)-The star converts hydrogen to helium in its core, generating heat and light. The next phase it will go through is the red super-giant phase. As nuclear fuel becomes depleted, the core contracts and the outer layers expand. Next the star will become a supernova. The core collapses in an instant. The repulsive electrical forces between in the core overcome the gravitational forces, causing a massive, short-lived explosion which blows away the star's outer layers. The next phase that Sirius will go through is the Neutron phase. It contracts tremendously into a small, dense object with an extraordinarily strong magnetic field, and a rapid spin. These are the phases it has to go through, leading to its death.

(C)-

The data provided data for these planets suggests that they does not follow Kepler's laws because according to kepler

T^2a^3

This law comes from inverse square law.

In an inverse square law holds only if there are two bodies or the effect of other bodies can be considered as negligible.

In this case the gravitational interaction is so strong between these planets so it can't be considered negligible because they are too close to each other.

(D)-

Astronomers found that the stars which are far away from the centre of the Galaxy aur orbiting with the same speed that the star which orbiting near from the centre of the Galaxy.( I am attaching a curve which may help)

So they concluded that there has to be something which is preventing this stars to go into intergalactic space and holding them together to form a galaxy. That thing is indeed dark matter.

Our galaxy does have enough dark matter that's why milkyway still exists, because the normal matter would not be able to hold the stars which are far away from the centre of the Galaxy.

So the measurements taken by students says that stars that are 6.8 kpc and 10.4kpc has aproximately the same speed. So we can conclude that it's the dark matter which is keeping them circumscribed in our galaxy.