Astro 150 Trivia - March 8

Which is true about interstellar medium (ISM)?

• It's made out of mostly gas and 1% of dust, too.

• Its average density is a few atoms per cc

• It is not uniform, but very clumpy

• All of them

Which of the following corresponds to the different interstellar medium (ISM) components in order of increasing temperature?

• Ultra-hot ISM, HI Clouds, HII Regions, Giant Molecular Clouds

• Giant Molecular Clouds, Ultra-hot ISM, HI Clouds, HII Regions

• Giant Molecular Clouds, HI Clouds, HII Regions, Ultra-hot ISM

• Giant Molecular Clouds, HII Regions, HI Clouds, Ultra-hot ISM

In what part of Interstellar Medium (ISM) can we observe in x-rays?

• Ultra-hot Interstellar Gas

• Giant Molecular Clouds

• HII Regions

• HI Clouds

Answer explanation

Ultra hot Interstellar gas is heated by the exploding stars. It heats up to millions Kelvins, so it can be observed by x-rays.

In what part of Interstellar Medium (ISM) are stars born?

• Ultra-hot interstellar gas

• HII Regions

• HI clouds

• Giant Molecular Clouds

Answer explanation

Giant molecular clouds are very dense and very cold, which is the best place for stars to be born by gravity.

The (wavelength) 21cm line is produced by electrons flipping its spins. In what part of the ISM do astronomers use the 21cm line to observe?

• Giant Molecular Clouds

• HII Regions

• HI Clouds

• None of them.

Answer explanation

The 21cm line is produced by an electron in hydrogen atom. HI Clouds consist of neutral hydrogen atoms.

Which one is true about dust grains in the ISM?

• Many of them will eventually end up in planets.

• They scatter light.

• It absorbs light and emits as a blackbody

• All of them are true.

This is the visible and near-infrared images of the cloud Barnard 68. The dark regions are produced by

• Black hole at the center of the cloud

• Interstellar dust grains that make the region opaque

• less dense regions of stars

• the defect in the telescope.

Answer explanation

Dust grains obscure light from the stars at visible and near-infrared wavelengths, a process called dust extinction.The obscuration caused by the dust diminishes dramatically with increasing wavelength (i.e., transparent at 2.16μm).

Protostars have outward pressure that tries to stop gravitational collapse. What is responsible for the outward pressure?

• Heat released by gravitational contraction

• Hydrogen fusion into Helium

• Helium fusion into carbon

• Nuclear fission of Uranium-235.

Answer explanation

Protostars are slowly contracting by their gravity. Gravitational potential energy is converted to heat while contracting, giving rise to outward pressure and allow them to shine.

What is the physics behind the formation of the disk surrounding a protostar?

• Faraday's law

• Conservation of angular momentum

• General relativity

• Kepler's 3rd law

Answer explanation

Angular momentum (proportional to radius and angular velocity) is conserved during the collapse. So as collapsing, material around a protostar spins faster and forms a disk.

Even though fusion hasn't activated in a protostar, why is a protostar more luminous than a main sequence star?

• Protostars are not more luminous

• They are much larger than main sequence stars

• Gravitational contraction releases more heat than fusion

• It's because of the heat released from all the surrounding gasses