Questions tagged [galaxy]

Questions regarding systems of large numbers of stars held together by gravity.

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0answers
57 views

Galaxies stay at same place but it's the space that splits the galaxies apart

Galaxies stay at same place but it's the space that splits the galaxies apart. Is my understanding correct? As per my understanding. Galaxies moving apart at high speed is due to the increase in ...
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32 views

What's so interesting about Coma-type galaxy clusters?

When the dynamical mass of a proto-cluster of galaxies is ~(1-2)x1014 Msolar, the proto-cluster is expected to evolve into a coma-type cluster. In almost every paper I read about the confirmation of ...
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15 views

How does the specific angular momentum - mass relation arise?

I'm reading about the specific angular momentum - mass relation of galaxies, and I'm confident I understand what the possible reasons are for the difference in specific angular momentum of ellipticals ...
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21 views

What is the highest redshift a galaxy with a known stellar mass can be observed?

As part of my research, I would need the following information which it seems I cannot find it in literature. I would like to know what are the highest redshifts at which $10^{7}$, $10^{8}$, and $10^{...
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36 views
+50

Interpretation and understanding of the relation for the photometric redshift in a given bin

In the context of photometric probe of surveys (like LSST), I need to understand the relation I have to use for photometric bins. Considering $p_{ph}(z_p|z)$ the probability to measure a ...
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1answer
101 views

Does IC 1101 have any name?

IC 1101 is the single largest galaxy that has ever been found in the observable universe, but does IC 1101 have any other name or at least a nick-name, perhaps something more soothing to the ear and ...
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94 views

How small can a spiral galaxy be?

The smallest observed spiral galaxies I can find are NGC 2976 and NGC 4605, both with a diameter of 20 kly, but I don't have anything like an exhaustive source to search. I've also found a mention ...
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1answer
74 views

Volume of Galaxies

Pretty much awkward question though. I would like to ask how is the volume of a Galaxy X is measured? For example consider milky way, what are the techniques to measure the same? How accurate and ...
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1answer
66 views

Calculate how long it takes for the sun to complete one orbit around the galaxy?

We know the speed that the sun travels around the galaxy is 220km/sec = 0.00021 parsec/year. I'm unsure of how to find the period?
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23 views

What are Stokes parameters for galaxy shapes, how do they compare to Stokes parameters in optics?

I remember Stokes parameters as a way to completely define the polarization state of a well-defined beam of light. However several questions here refer to Stokes parameters used in characterizing the ...
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16 views

How to get data on Low mass x-ray binaries in M31 (Andromeda) Galaxy?

So my question is pretty straight forward, I am currently working on a project on finding X-ray emission counterparts for optically observable objects and was trying to get data on Low mass x-ray ...
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87 views

Why aren't there blue elliptical galaxies or yellow spiral galaxies?

Elliptical galaxies are universally old and yellow; about three-quarters of all ellipticals have no significant star-forming gas or dust left, and even the quarter or so of ellipticals that are still ...
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“Radcliffe Wave” & filamentary dust structures

A recent paper by Joao Alves et al describes a kpc-long dust filament with a long, thin dust structure with vertical sinusoidal wave component. From the limited art work that accompanies it, this ...
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49 views

Is the angle of the Earth's orbit on the Galactic plane changing (towards 180 degrees)? [duplicate]

Currently the angle of Earth's orbit is aroun 60 degrees on the Galactic plane. But is this angle changing?
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2answers
3k views

Why don't they make an image of the black hole in the M33 galaxy?

Since we see the Triangulum galaxy M33 from a quite vertical position (contrary to our Milky Way and a bit the Andromeda galaxy) it should be easy to image the black hole in the center of it, shouldn'...
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1answer
59 views

Can the gravitational potential in a spiral galaxy be positive?

Thinking about this question I wanted to start with a rough model of the average gravitational potential of the Milky way. I ran across D. P. Cox and G. C. Gomez 2002 Analytical Expressions for Spiral ...
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17 views

Why does the star formation rate correlate with the total stellar mass in star forming galaxies?

The so-called "Main Sequence" of star-forming galaxies (e.g., Brinchmann et al. 2004; Noeske et al. 2007) clearly points to a linear relation between the stellar mass of galaxies and their star ...
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34 views

Minimum apparent magnitude of galaxy

currently I'm working on astronomy problem which deals with finding redshift of a galaxy. But the first part asks to derermine apparent magnitude of a galaxy: Find what should be the minimum ...
2
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1answer
55 views

What does Sa and Sab mean for spiral galaxies?

I have learned that the notation to classify spiral galaxies in the De Vaucouleurs system goes like "SA for spirals without bar, SB for spirals with bar and SAB for intermediate spirals". But in some ...
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0answers
54 views

Is there a galactic main sequence?

Stars can be plotted on an HR diagram, on which a main sequence is apparent, and stellar evolution can be plotted on on such a diagram as a function of mass. Is there an analog for galactic evolution? ...
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28 views

Must all galaxies in a galaxy cluster have the same expansion rate?

If we observe a distant galaxies cluster where all galaxies travel with the same speed away from us, except for one galaxy whose speed is significantly lower than of the neighboring galaxies. Does ...
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1answer
99 views

How do galaxies move in space?

Kind of like a shower thought just occurred to me. We've all seen lots of animation about spiral galaxies, how they crash... in virtually all of them, I recall they move in a frisbee way, that is ...
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1answer
42 views

How do disk-shaped galaxies then form at the sites of spherical galactic halos? Do the halo stars start orbiting or just sit in place?

Phys.org's Astronomers detect large amounts of oxygen in ancient star's atmosphere mentions "Stars like J0815+4729 are referred to as halo stars," explained UC San Diego astrophysicist Adam ...
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56 views

How many galaxies have had their distance determined using SNIa?

Supernovae of type Ia can be used as standard candles to determine extra-galactic distances. But these event only occur (roughly) once every 200 years in any given galaxy and rapidly fade away. So to ...
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25 views

Large-Scale instabilities in Disk Galaxies

Multiple sources in literature state that a disk galaxy, without considering the presence of Dark Matter is subject to large-scale instabilities. What is the reason behind the claim? I am looking for ...
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How the depth[Mpc] is obtained from the redshift

I read this paper. In this paper, they show the three-dimensional distribution of the [OII] emitters. It is mentioned that The depth in z-axis is converted from the redshift, which is estimated from ...
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71 views

In the milky way which star(s) are farthest from galactic plane?

I am looking for at least one star on each of the side of the galactic plane. I understand there would be an error tolerance. So, please do not hesitate if the answer is not exact. Preferably, please ...
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1answer
56 views

What is the current angle of motion of the sun with respect to the Galactic Plane?

I understand that the solar system oscillates in its motion around the Milky Way. However at any given time, there must be a specific angle between the current direction of the solar apex and the ...
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1answer
44 views

Correlation between stellar mass and galactocentric distance

As we move away from the centre of, say, a spiral galaxy, is there a relation between the stellar mass and distance? I know the how the stellar abundance and density varies with the distance but does ...
2
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1answer
53 views

Elliptical galaxy morphology

I understand what differentiates elliptical galaxies from spiral, lenticular, and irregular galaxies. What is the difference between a compact elliptical (cE) galaxy and a dwarf elliptical (dE) galaxy?...
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0answers
49 views

Does the axis of solar system precess during it's motion in the Milky way galaxy?

The plane of solar system makes an angle of 60° with the plane of galaxy. So, the axis of solar system should make 30° angle with the galactic plane. Like the axis of Earth precess over a long period, ...
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1answer
34 views

What are the smallest star clusters affected by Galaxy Rotation Curve?

We all know that Milky Way exhibits Galaxy Rotation Curve which makes it rotate very differently that Newtonian mechanics would expect. But Milky Way is a pretty large galaxy, and the one we only see ...
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4answers
85 views

How are galactic rotation curves determined from radial velocity measurements?

I have been reading about the deviation of galactic rotation curves from the predicted Keplerian curve to a flat curve at large galactocentric distances. They were the first indicators of the ...
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23 views

Doppler Shift Vs Gravity Assist for Frequency Shifts from Rotating Galaxies

Frequency Shift of Light Leaving Rotating Galaxies: Differences in Doppler Shift due to Radial Velocity Vs Frequency Shift due to Gravity Assist from a Rotating Galaxy A description of estimating ...
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2answers
97 views

What percentage of a spiral galaxy is the center/bulge?

Is there a credible source that can tell me how big the bulge of a spiral galaxy is compared to the rest of the galaxy? Unfortunately, I could not find any.
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2answers
4k views

Why does the 70-solar-mass black hole in the LB-1 system challenge current astrophysics?

Recently scientists discovered a large stellar-mass black hole, which (previously) they believed that it shouldn't be possible in our galaxy! Source An international team of scientists say they ...
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0answers
132 views

“Holes” discovered in the Milky Way Galaxy

Recently I read that Astronomers have noticed a few "holes" in our Galaxy. They are about one million times the mass of our Sun. They are baffled as to what could have caused this and speculate that ...
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1answer
57 views

Can we measure stellar accelerations?

Many people concern themselves with understanding the Galactic potential. To me, the most obvious way is to measure the acceleration of a star, as this is directly related to the potential. So, one ...
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1answer
60 views

When is the best time to observe M81 from the Northern Hemisphere?

I have read that the best time to view M81 is during the spring. Considering its RA is ~10h and Dec. is +69°, wouldn't February 21st be the best time to view it since this is about when it transits my ...
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2answers
719 views

Are there any galaxies visible in the night sky around the Orion constellation?

I'm writing a story for NaNoWriMo, and in it there is an extraterrestrial race whose home galaxy is visible from Earth. This home galaxy is visible (or even partially visible or barely visible) in the ...
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1answer
110 views

What is the distance between the solar systems towards the center of galaxy?

The distance from our Solar System to the nearest is roughly 260,000 AU. I am wondering what is the minimum distance between two Solar Systems. Since the center of our galaxy is supposed to be more ...
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1answer
60 views

How to convert from FELO-HEL to Km/s?

I am using DS9 to calculate the rotational velocity of a galaxy. I have 21cm cube and I used DS9 to plot this graph I do not understand what is FELO-HEL! and I want to convert the units from FELO-...
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2answers
67 views

Photometric redshift - empirical methods (machine learning)

I am currently learning about estimation of photometric redshifts with machine learning methods (or empirical methods in general). These methods use the knowledge about the photometry and the ...
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0answers
69 views

What is the history of the Milky Way's relationship with Andromeda?

From what I've read, the Milky Way will collide with Andromeda in about 4 - 5 billion years, and a billion or so years after that the two will merge and become a giant elliptical galaxy. What I'm ...
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46 views

What is the largest cluster of merging galaxies?

Reading about the Andromeda–Milky Way collision, a galactic collision predicted to occur in about 4.5 billion years between the two galaxies, I went to the galaxy merger page and Wikipedia states that ...
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1answer
160 views

From what distance will be able to see milky way and andromeda collision? [closed]

Considering that we would out of Milky Way, at what distance would a human will be able to see the collision with naked eye and and how fast would the galaxies appear to be approaching each other
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0answers
109 views

What is the meaning of ellipticity of a galaxy being more than 1?

I was recently doing a project on calculating ellipticities of galaxies using SDSS data. I downloaded the stokes parameter values (q and u) from data $e = 1 - \frac{b}{a} = 1 - \frac{1 - \sqrt{Q^2 + ...
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1answer
150 views

Do gravitationally bound (e.g. orbiting) objects really resist the expansion of space?

Thinking about the expansion of space, it is commonly explained that gravitationally bound objects (like galaxies and galaxy clusters) will not be affected by the expansion of space (dark energy). I ...
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1answer
246 views

Will intergalactic travel be impossible in roughly 15 billion years?

Even if we (or aliens somewhere in the universe living at that time) somehow invent something that can go just short of the speed of light, will intergalactic travel still be impossible in roughly 15 ...
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104 views

What decides the shape of a galaxy?

As I know, most galaxies are spiral, some elliptical, and a rare type is ring-shaped. What causes a galaxy to become a specific shape (i.e. ring vs spiral)?

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