[AstroTech/6주] 시험

[AstroTech/6주] 시험

Question 1
In the lectures, you've learnt our Universe has both a normal and Dark side! Can you choose the option that specifies the percentages and nature of the different components our Universe is made up of?

()5% normal matter, 25% Dark matter that tries to pull things together through gravity and 70% dark energy that is expanding the Universe at a decelerating rate.
()50% normal matter, 25% Dark matter that tries to pull things together through gravity and 25% dark energy that is expanding the Universe at an accelerating rate.
()5% normal matter, 70% Dark matter that tries to pull things together through gravity and 25% dark energy that is expanding the Universe at an accelerating rate.
(o)5% normal matter, 25% Dark matter that tries to pull things together through gravity and 70% dark energy that is expanding the Universe at an accelerating rate.

-> As Catherine has explained, the Universe is mostly made up of dark matter (25%) and dark energy (70%), with only 5% being normal matter that we are all made up of!

우주는 25%의 암흑물질(중력작용을 함), 70%의 암흑물질(우주를 팽창시킴)로 이루어져 있고 관측할 수 있는 것은 겨우 5%에 불과 함

Question 2
Andy told us how important spectroscopy is to study astrophysical objects. Of the choices given, pick all that describe the advantages spectroscopy can provide.

()Spectroscopy can be used to find the earliest galaxies more easily than imaging.
(o)Spectroscopy can be used to measure the velocity an object is moving with.
()Spectroscopy is the best way to find Supernovae.
(o)Spectroscopy can be used to infer the chemical composition or make-up of an object.

스펙트로 스코피로 알 수 있는 것,
- 천체의 화학적 조성(스펙트럼 흡수선/방출선)
- 천체의 움직이는 속도(도플러 효과)


Question 3
Catherine told us about the wonderful Supernova Ia (SN Ia) that are called "standard candles" and used to measure distances in cosmology. What is the reason that these objects are standard candles?

()SN 1a have the same apparent brightness no matter how far away they are from us - this is why they are called standard candles.
()SN Ia are everywhere in the Universe so they are called standard candles.
()SN Ia form when a red giant explodes on reaching a critical mass of 1.4 solar masses. Since all SN Ia explode at the same mass, they produce the same luminosity, marking them as "standard" candles.
(o)SN Ia form when a white dwarf explodes on reaching a critical mass of 1.4 solar masses. Since all SN Ia explode at the same mass, they produce the same luminosity, marking them as "standard" candles.
-> Supernova Ia form when a white dwarf explodes on reaching a critical mass of 1.4 solar masses. Remember it is the white dwarf that sucks matter from the red giant, not the other way around!

초신성은 백색왜성이 주변의 적색거성을 끌어들여 정확히 태양 무게의 1.4배가 될 때 폭발. 이 무게의 폭발은 밝기가 정확하게 일치함.


Question 4
Doing spectroscopy of a large number of objects is really slow. The best way to improve this is by: (pick one answer)

()integrating/looking at a galaxy for shorter times
(o)using multiple fibres to look at many sources at the same time.
()using bigger telescopes
()integrating/looking at a galaxy for longer times

수많은 별에 대해 일일이 스펙트로스코피 관측이 어려우므로 망원경의 촛점면에 광섬유 다발을 장착. 컴퓨터 제어를 통해 광섬유를 교체해가며 관측 기록


Question 5
All star-forming galaxies produce a Lyman Alpha Emission line at a wavelength λemit=121.6 nm when the electron in a Hydrogen atom falls from the first excited state to the ground state. The energy produced by this transition is E = 10.2 eV. Imagine a galaxy at a redshift of z=9 that produces a Lyman Alpha line. As an observer on earth, what observed wavelength (λobs) and energy would we measure for this line? Remember E=hcλ.

()λobs=12160 nm and E = 1.02 eV.
(o)λobs=1216 nm and E = 1.02 eV
()λobs=1216 nm and E = 10.2 eV.
()λobs=12160 nm and E = 10.2 eV.

If you take the formula Catherine gave for redshift and play with it a bit, you will find that the λobs=λemit(1+z) , i.e the wavelength observed = wavelength emitted * (1+z)

z = (λobs - λemt)/λemt

계산해보면 됨.