Do Irregular galaxies form stars?

Question

And, question #2 - if a black hole were seen nearly directly towards a background star, what would we observe?

Answer 1

Irregular galaxies refer to the shape of the galaxy itself. These are formed when two galaxies collide, destroying the spiral shape and forming an irregular (as opposed to a regular, or symmetric) shape.

"Collision" is not the best word. While the galaxies themselves get distorted, few if any stars actually collide. Instead, they are flung all over the place due to gravity. Gas is also flung everywhere, and again because of gravity the gas collapses, in turn initiating huge amounts of star formation after the collision. So yes, there is definite star formation in irregular galaxies.

If a black hole were between us and a background star, the light of the star would be bent around the black hole. The extremely compact mass would form a "gravitational lens", which was predicted by Einstein and has been observed multiple times (usually its a galaxy in front of a very distant second galaxy). The gravitational lens would form 2 or 4 images of the star, symmetric around the black hole at the center, which would (of course) be devoid of light. Because the star lies directly behind the black hole, these images would be an equal distance from the true position of the star, in the N, S, E, and W cardinal positions.

Answer 2

Question One: Do irregular galaxies form stars? Irregular galaxies are usually rich in gas and dust. They are shapeless collections of stars. They do not "form" stars. The stars are what make up a "galaxy." Inside irregular galaxies many black holes and new born stars may be found. Lots of unusual emissions may be detected from these irregular galaxies as a result of the birth of new stars. Irregulars called "starburst" galaxies are the most prolific in birthing of new stars.

Typical irregular galaxies you might wish to investigate further are "LMC" in the Dorado Constellation, and "SMC" in the Tucana Constellation.

Galaxies have four major types:
Spiral, Barred Spiral, Eliptical, and Irregular.

In Spiral Galaxies, a central hub is dominated by old red and yellow stars, and surrounded by gas and dust rich spiral arms. The space between the arms is not empty. It contains a scattered mix of different kinds of stars. The arms are prominant because they contain the brightest and most short lived stars. The arms are regions of increased density that sweep around the disk triggering new starbirth as they go.

In Barred Spiral Galaxies the hub is crossed by an elongated bar of stars from which spiral arms emerge. It is also possible that our own Milky Way Galaxy is a Barred Spiral Gaqlaxy. The bar just happens to be aligned with our point of view from Earth.

Elliptical Galaxies come in a wide range of sizes. They are huge balls of mostly old red and yellow stars, each of which follows its own elliptical orbit around the center. These galaxies contain very little gas and dust, so little or no new star formation is occurring within them.

Active galaxies are the sum of their stars. The radiation they emit comes from their individual stars. Quazars and Blazars are extremely distant galaxies in which most of the radiation comes from a small, rapidly varying region around the hub.
Seyfert galaxies resemble normal spiral galaxies but have much more brighter cores than one would expect to find.
Radio galaxies are usually insignificant galaxies surrounded by huge lobes of gases which emit radio waves.

Astronomers think that all these different types of activity are caused by the black holes at the center of the galaxies. While the black hole in the center of most galaxies is dormant, in others the black hole is still consuming material.

Question 2. Were a black hole aligned with a background star we would probably not be able to see the star in the background. massive activity around the black hole would cause this, and light does not seem to exit out of black holes. Therefore, any light emitted by the background star would probably be interrupted on its pathway to our eyes or telescopes.

I highly recommend that you try to locate a copy of the book,
ASTRONOMY, by Ian Ridpath, DK Publishing, NY, NY. That book has some of the best illustrations of galaxies, and star types I have seen. Mr. Ridpath also places a block of easily understood text with each photo or illustration so the readers can fully appreciate what he is saying. I bought one copy of that book and refer to it often.

Answer 3

The magellanic clouds are irrigular galaxies orbiting our galaxy that contain star-forming regions.

#2 - gravitational lensing