# Tag Info

58

The object which has less mass and gravitational pull orbits around the nearest object with more mass and gravitational pull. Actually, both the heavier and the lighter object orbit around their common center of mass. It's just that the heavier object doesn't move much (has a tiny orbit), while the lighter object moves a lot (has a wide orbit). E.g. our ...

44

What is a spiral arm? The reason that the Sun, in principle (but see below), may cross spiral arms is that galactic spiral arms are not rigid entities consisting of some particular stars; rather they are "waves" with a temporary increase in density. An often-used analogy is the pile-up of cars behind a slow-moving truck: At all times, all cars are moving ...

37

Galaxies move through space with velocities of the order of a several 100 km per second; small velocities for small groups (~100 km/s; e.g Carlberg et al. 2000) and large velocities for rich clusters (~1000 km/s; e.g Girardi et al. 1993). In addition to this so-called "peculiar velocity", galaxies also also carried away from each other due to the expansion ...

35

There are several clues. The Milky Way is a flat disk The first one, and the simplest one, is that we live in a disk. As you can see on images like the ones from the 2MASS survey in the infrared range: We clearly see that we are inside a disk, since what we see when we look around us is a disk seen edge-on. It does not look like an ellipsoid or any other ...

31

There're several pieces of information one needs to understand this. Although stars more massive than 70 solar masses exist, when they become black holes, they usually lose mass in the process. The exact amount of mass lost depends on the metallicity (which is a technical term that describes how much "metals" - the astronomer's definition of metals is ...

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I wholeheartedly recommend astrometry.net for this sort of thing. It Just Works(tm); running on your image produced this output with absolutely no hints or guidance from me: For avoidance of doubt, I have no association with astrometry.net.

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I'll turn my comment into a full answer. To put it simply, we actually do see the Milky Way all around us, even in the diametrically opposite direction from the galactic core. You can see this in the image below which is a full sky image I took from APOD. If you look at the edges of the disk in that image, you're looking at what is actually the edge of our ...

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Presumbably we rotate beacuse of the BH. No. The galaxy is being held in one piece due to its own total gravity. The black hole is only a small fraction of that. Basically, the BH doesn't matter. When the black hole dies in our galaxy The BH will probably be the last thing left of our galaxy at the end. And even then it will take some incredibly long ...

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Here's a rough sketch of the Milky Way and the Andromeda galaxy,* showing their approximate sizes and distance from each other to scale:   What the picture (hopefully) illustrates is the incredibly vast gap of empty space — around 2.5 million light years, to be exact — between the galaxies, each of which has a diameter of only(!) around ...

24

The sun is within a few parsec (15-25 pc) of the galactic plane, slightly above. The thin disk of the milky way (containing ~85% of the stars and gas) has a density going roughly like $\rho_0 \exp(-|z|/300 pc)$, while the thick disk (older stars, a few percent) has a scale height of 1000 pc instead. So if we want to move up (galactic north) above 90% of the ...

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What will happen to life on earth or human beings on earth? Assuming that human beings, or life, still exists on Earth at that time, they will have survived so much due to the ongoing death of the sun, that the gravitational pertubations due to the galactic collision will be nothing. Keep in mind that in about 1-2 billion years, the sun will be so hot and ...

23

The orbital elements are on wikipedia: $$e=0.884\ a=0.125'',\ i=134^\circ,\, \Omega=228^\circ$$ (At an assumed distance of 8kpc, $0.125'' = 1000au$) It is the inclination that means that the black hole is not at the focus of the projected ellipse. Imagine a circular orbit, with a central body. If viewed from a distant but high inclination, the orbit is ...

22

We are situated inside the galactic disk. The first image below, showing our approximate location, is a fabrication rather than a photograph. Such a photo would require a space probe to be tens of thousands of light years above the plane of the disk, which is patently infeasible with current technology. We don't even know exactly how many spiral arms our ...

22

Answer: Not much The Milky Way's central black hole (BH) masses about 5 million suns, while the galaxy masses 100 billion to a trillion suns. Consequently, the central BH is pretty much irrelevant to the dynamics of stellar orbits except very close to the center. But what do you mean by "the black hole dies"? Do you mean evaporates through Hawking ...

21

The Milky Way Galaxy is a large spiral galaxy with some characteristic features worth mentioning: 1) The bulge - This refers to the collection of tightly packed stars located in the central region of the galaxy. 2) The spiral arms or the disk - This region extends from the inner region of the galaxy (where it meets the bulge) to outskirts of the galaxy, ...

21

Humphreys & Larsen (1995) suggest, using star count information, a distance of $20.5 \pm 3.5$ pc above the Galactic plane; consistent with, but more precise than the Bahcall paper referred to by Schleis. Joshi (2007) is more guarded, investigating some systematic uncertainties in the estimation techniques and ends up with distances between 13 and 28 pc ...

21

This is actually a really, really tough question. Look at this diagram: Purple: Norma Arm and Outer Arm. Green: Scutum-Centaurus Arm Pink: Carina-Sagittarius Arm Cyan: 3 kpc Arm and Perseus Arm So we can slightly modify this picture by saying that there are four arms, and calling them by the following names: Norma-Outer Arm This arm has one end at ...

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4 billion years is the same timeframe of the life remaining to our Sun. So if we have not yet invented interstellar voyages, we're screwed, with or without Andromeda. Besides, stars do not interact directly with each other in a galactic collision. What we will notice from the several stars we are on is that star orbits around the galactic centre will be ...

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First, note that by the time Andromeda is close enough for collisions with wandering stars to become a concern, Earth's average temperature will have changed significantly, and the planet will be unrecognizable. When Sol is 8.5 billion years old, it will still have hydrogen available for fusion, but as it fuses it contracts and expands differentially. The ...

16

The main reason we don't see the bright center of our galaxy, which is composed of millions of stars, is dust. Visible light is absorbed and scattered by interstellar dust, but that doesn't mean we can't see it on other waves of the spectrum, for example, infrared light doesn't suffer as much because of the dust. Notice on this image how bright the galaxy ...

16

With the exception of the Andromeda galaxy and the Magellanic clouds1, every star, star cluster and nebula that is visible to the naked eye is part of the Milky Way. The Pleiades is a star cluster in the Milky Way. Objects in other galaxies are too far and too dim to be visible with the naked eye. 1The Triangulum galaxy (M33) may also be visible to the ...

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There are several different lines of evidence which together form a coherent picture: that of a barred galaxy. Moreover, as most disc galaxies are barred, we should expect the same from the Milky Way. The various evidences are: The observed light distribution (2MASS) shows a left-right asymmetry in brightness and the vertical height. This is explained by ...

15

Photos of the galactic center aren't too bright because of all the gas and dust between us and it. For example (in infrared): I'm guessing, though, that you're talking about other galaxies, because there are no views of the galactic center of the Milky Way face-on. Although the galactic center is pretty luminous, just not in the wavelengths we're used to. ...

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The Galactic Coordinate system is a longitude-latitude coordinate system that is used to define the positions of objects in space, most commonly objects within our own galaxy. It uses the center of our galaxy as the focal point (i.e., where we consider $(0^{\circ},\:0^{\circ})$), much like we use the position just off Africa as the focal point of the Earth's ...

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The Sun moves, even in the context of the solar system. Gravity of the planets (mostly Jupiter) pulls the Sun out of position with respect to the centre of gravity of the solar system. This wikipedia entry explains it in a lot more detail, and also explains that their common centre of gravity lies outside of the sun. This wobbling of a star due to planets ...

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The paper in question is now on the arXiv here: "Detection of the Schwarzschild precession in the orbit of the star S2 near the Galactic centre massive black hole". This gives the following orbital elements (Table E.1): a = 125.058 mas e = 0.884649 i = 134.567° ω = 66.263° Ω = 228.171° The orbital elements $i$, $\omega$ and $\Omega$ are essentially ...

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Not really, for the same reason that you cannot travel west by jumping up in the air and let Earth rotate underneath you, such that you land a little farther to the west. The reason is that standing on Earth's surface, you already have a velocity toward the east which matches exactly the speed of the surface. Thus, in the reference frame of Earth, you ...

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Absolutely nothing left. The time for stellar black holes to evaporate is said to exceed the proton half life. How much more the galactic black holes. And by the way, this time is currently increasing as even stellar black holes are currently growing from the cosmic background radiation alone. The universe must pass through the intermediate phase of black ...

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As has now been corrected, BBC has misunderstood term "Seyfert flare", instead calling it a "Sifter flare". A "Seyfert flare", is not really a common term, but the authors refer to an energetic outburst from the type of active galaxies called Seyfert galaxies (after Carl Seyfert). Like a quasar, a Seyfert galaxy is powered by gas accretion onto a central, ...

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