25
votes
Accepted
Is it possible that a star is the center of a galaxy?
It won't stay in the center for long.
Galaxy nuclei are full of stars. Any star passing by will exchange momentum with the central star and will perturb its position. Stars of similar mass will be ...
- 2,879
23
votes
Is it possible that a star is the center of a galaxy?
The short answer is, not really. Galaxies are unlikely to have a star at the "center".
When you say a star is at the center, what you're really trying to say is that that star is the ...
- 15.1k
15
votes
Is it possible that a star is the center of a galaxy?
Galaxies are gravitationally bound by the mass of all the stars, gas, dust, planets, black holes and "dark matter" that they are made of. In fact the majority of the mass comes from the &...
- 129k
12
votes
Accepted
Do all galaxies have a black hole in the center?
The answer here is certainly no. Many dwarf galaxies (e.g. the Magellanic Clouds) don't contain supermassive black holes, although some may contain less massive intermediate-mass black holes (Mezcua ...
- 37.4k
11
votes
What is the escape velocity of our Galaxy relative to?
One way to think of the Escape velocity is to imagine it backwards.
Instead of a rocket being fired into space, think of the same rocket, starting at rest relative to the Earth at a great distance (...
- 129k
10
votes
Accepted
How bright would the night sky be in the galactic center?
Interesting question. Assuming the figure of 10 million stars per cubic parsec is correct, there's still one missing piece of information to try getting a estimate: The size of this region with a very ...
- 1,201
9
votes
Revolution of the sun
The Sun orbits in the entire Galactic gravitational potential, which is very approximately similar to that provided by considering that all the mass interior to its Galactic orbit (about 100 billion ...
- 163k
8
votes
Accepted
Could a dwarf galaxy host a star at the center instead of a SMBH?
A galaxy's center of gravity is not determined by the most massive object, but by all objects in the galaxy. Even supermassive black holes (SMBHs) do not dominate the gravitational field except very, ...
- 39.6k
8
votes
Accepted
How can I convert my sky coordinate system (RA, Dec) into galactic coordinate system (l, b)?
Applying spherical trigonometry, it follows that the conversion from equatorial coordinates $\alpha$ and $\delta$ to galactic coordinates $l$ and $b$ is:
$$\left.
\begin{aligned}
\sin b &=\sin \...
- 2,294
7
votes
Accepted
What percentage of a spiral galaxy is the center/bulge?
The term you're looking for is called the bulge-to-disk (size) ratio. Sort of by definition, the answer depends on the morphology of the galaxy, i.e. how "late-type" spiral it is. "Sa" spirals are the ...
- 39.6k
7
votes
What is the escape velocity of our Galaxy relative to?
James K's answer is great, I just want to offer a few definitions:
Any mass $M$ — whether a be point mass like a planet or an extended mass like a galaxy — has an associated gravitational potential $\...
- 39.6k
7
votes
Accepted
When we say the sun takes 230M years to orbit the galaxy, what is this in relation to?
The Sun's velocity is known (with uncertainties) with respect to the Galactic centre (GC), as is the Sun's distance from the Galactic centre. These measurements have a long tortuous history, which I ...
- 163k
6
votes
What percentage of a spiral galaxy is the center/bulge?
To answer the title question, what you want to know is the bulge-to-total ($B/T$) ratio, which is the fraction of a spiral galaxy's light (and thus, approximately, its stars) which in the bulge; this ...
- 18.4k
6
votes
Accepted
Behaviour of black holes
No, it seems that the formation of a supermassive black hole is a consequence of galaxy formation, not a cause of it. The mass of the black hole is a very small proportion of the mass of the matter ...
- 129k
6
votes
Accepted
Why can I see the Andromeda Galaxy despite Milky Way's rotation?
As barrycarter already pointed out, it is due to the huge time it takes for the milky way to rotate.
For once, as he pointed out, the stars in an orbit similar like the sun take about 250 million ...
- 453
6
votes
Do all galaxies have a black hole in the center?
It's generally assumed that most galaxies have a black hole at their centre. There are galaxies we've detected that don't seem to have a black hole though, so it's not a necessary requirement or a ...
- 243
4
votes
What is that light of the middle of the milky way galaxy?
The galactic bulge is formed by tightly packed stars and interstellar dust
Also most stars are in the direction towards the galactic center
Thus it would appear brightest if it were viewed from ...
- 381
4
votes
Why is the Milky Way called like that?
Milky way obviously is an English word with that literal meaning a way (path) covered in milk. So it's not exactly derived. But it is a literal translation from Latin 'via lactia' and the Greek ...
- 21.4k
4
votes
If our galaxy is mostly empty space then why does it look so solid?
You are mostly empty space. Every atom in your body is very tiny compared to the relatively vast spaces between it and its nearest neighbors. And the same goes for every "solid" object you ...
- 8,037
4
votes
What object(s) are furthest above/below the galactic plane?
Bochanski et al. (2014; "The Most Distant Stars in the Milky Way") reported the discovery of two stars -- ULAS J001535.72+015549.6 and ULAS J074417.48+253233.0 -- found to be M giants at ...
- 18.4k
4
votes
How to plot object on the map correctly
No, it's not enough. The coordinates you give are the position in the sky. To plot a location in the galaxy, you'd need also to know the distance from Earth.
However, nearly all naked eye visible ...
- 129k
3
votes
Is it possible that a star is the center of a galaxy?
You've mis-remembered or mis-heard some things and got a bit confused. Let's try to fix that...
Supermassive black holes
We have discovered that most galaxies have a supermassive black hole at their ...
- 1,030
3
votes
SDSS - getting separate u, g, r, i, z frames from SWARP tool and astropy
What they did was the following: for each individual filter, they assembled overlapping frames into a combined, single-filter image. E.g., they combined several g-band images into a single g-band ...
- 18.4k
3
votes
Accepted
What coordinate system is at rest relative to the center of the galaxy?
Galactic coordinates are sun centred with a zero longitude chosen to align with the centre of the galaxy when the measurements were made in 1958.
As defined, the galactic coordinates don't rotate, and ...
- 129k
3
votes
Why can I see the Andromeda Galaxy despite Milky Way's rotation?
It is certainly true that the galactic orbit is very slow. Yet it should be noted that even if the Sun/Earth system orbited the galaxy once every century, the Andromeda galaxy would still be seen in ...
- 5,334
3
votes
Accepted
Extragalactic Magnetic Fields - General Information That I'm Missing
On this question, the Widrow (2002) review is still pretty up-to-date. You can also have a look on the introduction of Beck (2013), a recent PhD thesis on the subject with a straightfoward ...
- 5,543
3
votes
How bright would the night sky be in the galactic center?
From Foundations of Astrophysics by Barbara Ryden and Bradley Peterson (which I highly recommend):
If the Sun were half a parsec from the Galactic center:
. The nearest star would be ∼ 1000 AU away.
....
- 212
3
votes
What object(s) are furthest above/below the galactic plane?
Globular clusters orbit in the Galactic halo, and so are good candidates for being far above the disc. The globular cluster PSO J174.0675-10.8774 is the furthest, 470,000 light years distant, well ...
- 129k
3
votes
How can I convert my sky coordinate system (RA, Dec) into galactic coordinate system (l, b)?
This can be pretty easily accomplished in astropy using the following code:
...
- 1,642
2
votes
What is the movement of stars within the nucleus of a barred spiral galaxy
It's a little hard to know how to answer your question, partly because you're using "nucleus" in a confusing fashion. So let me try answering what might be your general question, which is "how do ...
- 18.4k
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