Science questions about space help please!!?

Question

1.) What evidence indicates that many quasars existed long ago??
2.) Why do astronomers hypothesize that there is a supermassive black hole at the center of the milky way?
3.) How do astronomers observe the spiral structure of our galaxy?

Answer 1

1 They have large red shifts, so we're seeing them at enormous distances and hence a long time ago. We don't see any nearby.

2 Stars near the centre are orbiting at high speeds - they must be orbiting something massive.

3 By measuring the intensity of the 21cm emission line from neutral hydrogen.

Answer 2

1) Astronomers can see the light (and radio waves) from quasars, and they can detect that the light is "red-shifted". The best explanation they have for this, is that the quasars are far away and moving fast. That means that it took a very long time for the light to get to us, which means that the light left the quasars billions of years ago. So ... the quasars must have existed billions of years ago.

2) Astronomers can detect the radio waves coming from the center of the milky way (Sagittarius A). The spectrum of this radio signal looks like what they expect to see from a black hole (actually, its the radiation from the dust falling into the black hole.) Also, the stars near Sag A orbit the way they would expect for a black hole.

3) By using radio telescopes.

The links below discuss all this.

Answer 3

1) All observed quasars "are" in very deep space. Since light travels at a limited speed, distance effectively equals time. A lack of nearer quasars indicates that there are no new ones.

2) Astronomers have observed the energy jets typical at the poles of large black holes in the area of Sagitarius in the center of our galaxy. That, combined with their observations of other spiral galaxies, leads them to believe there is a black hole at the center of our galaxy.

3) Careful observation and calculation of star positions shows waves of star concentrations in our sky, indicating a spiral arm structure. The most recent findings indicate ours is a barred spiral galaxy.

Answer 4

To answer the first question I would say the distance of objects and the length of time it takes their light to travel to the earth is a big clue as to their age. That a black hole may exist at the center of the milky way is perhaps the result of observations or the lack thereof of radiation passing through or near that region from more distant objects and affected by the presence of a black hole. The spiral structure I believe is deduced from the red-shift in radiation due to the relative differences in rotation across the galaxy.

Answer 5

1) They are billions of light years away, so we see them by the light then emitted billions of years ago.

2) They can see stars orbiting very close to the center of the galaxy in a way that would only be possible if there were a mass equal to billions of stars concentrated in an area not much bigger than our solar system, but nothing is seen there visually, although there is a strong radio source there, which is believed to be caused by matter falling into a black hole.

3) It is quite hard to see the structure of our own galaxy since we are inside it, but we can easily see it in other galaxies. To map the structure of our galaxy requires measuring the distance to many objects, like stars and gas clouds, and them making a map of them.

Answer 6

My info on this is quite dated, but I'll try:
1. quasars have a highly shifted light spectrum, hence are far away, therefore quite old.
2. Scientists will hypothesize on anything (joke).
3. You can determine distance and position by wide array telescope of many stars in our galaxy.

Answer 7

1) extremely high red shifts in their spectra which translates into great distances and that in turn implies extreme age http://www.geocities.com/newastronomy/quasars.htm

2)careful observation of the movement of stars and gases near the core of the Milky Way are consistent with an immense and localized gravitational field as would be generated by a super-massive black hole

3)the structure can't be observed directly, but by careful observation of motions of celestial objects in all directions from Earth along with the relative densities of dust and gases the spiral structure can be inferred.

Answer 8

1. Due to the redshift of the light from those.
2. Stars near the center of our Galaxy orbit the invisible center at speeds of about 1% of the speed of light (3,000 km/sec). From the speed and the distance to the center they can calculate how big a mass would allow such orbits.
3. By looking at different parts of our Galaxy and correlating that to the shape of other Galaxies.

Answer 9

Wow, some good answers No need from me to add tuppence worth.

It always surprises me how the level of question and answer varies so greatly on this forum.

Also, I wonder, if school curriculae have astronomy to this level, why are some kids still asking questions like "what causes the phases of the moon" or "why do some stars fall".