Hot answers tagged

31

Let's say we have a spherical shell of some material emitting light, much bigger than the star it surrounds. If we look right down the center of the shell, our line of sight takes us through only a small amount of gas - not enough for there to be significant emission. On the other hand, if we look at the nebula near the outer edge, our line of sight takes us ...


30

It appears to be static because it's huge beyond your imagination. The distance to the nebula is 7,000 light years. Its apparent size is 7 arc minutes. Therefore its linear size is about 14 light years. Think about that. The whole nebula is so big, it takes light 14 years to cross it. Any motion therein must necessarily be much, much slower. No wonder you'...


25

There are three main reasons why we can tell that local stars did not, for the most part, form from the same molecular cloud that the Sun formed from. The first is that unless stars are born in a very tightly bound system such as a globular cluster (which the Sun is definitely not in), they will drift apart from their birth companions over time in slightly ...


20

Short Answer Thin gas in a nebula only absorbs some portion of star light corresponding to a small subset of the overall visible spectrum, according to the corresponding molecular composition of the nebula. For even these limited spectral ranges, the star is still often visible in a nebula since the gas can be too thin to absorb all the energy emitted by the ...


19

To add to Florin Andrei's answer, with an image height of 7,000 pixels for 14 light years, that's 17.5 light hours per pixel. That's 20 billion kilometres per pixel. To make a change in a single pixel over that time, something of that size must have either changed composition dramatically (to give a different colour or opacity) or it must have moved by a ...


19

Is it possible that the Sun and all the nearby stars formed from the same nebula? No, it is not. Our Sun has marked differences in metals compared to the nearby stars. (In astronomy, every element higher than helium is a "metal".) The discovered and analyzed stars that appear to be most similar to the Sun are far, far away from the Sun. Our Sun ...


16

In the best sky conditions, the naked eye (with effort) can see objects with an apparent magnitude of 8.0. This reveals about 43,197 objects in the sky. There are 9 galaxies visible to the naked eye that you might see when observing the sky, and there are about 13 nebulae that you might see. Sources: The Bortle Dark-Sky Scale - John E. Bortle How many stars ...


15

Cosmic GDP has already crashed, as Peak Star was ~11 billion years ago. According to Sobral et al's prediction, the future star production by mass will give only 5% of the stars in the universe today, "even if we wait forever." More theoretical predictions, such as this one, suggest that nebulae will run out of hydrogen on the order of $10^{13}$ years, ...


13

Rudolf Minkowski. Its not likely to be the mathematician, Hermann. Nor the physiologist Oskar. There's only one Minkowski who was an observational astronomer. The paper describing M1-92 was https://iopscience.iop.org/article/10.1086/125855 The 2006 paper on Minkowski's object (Croft et al) cites Minkowski, R. 1958, PASP, 70, 143


12

Yes, indeed! Many nebulae are visible from Earth in a small and cheap telescope, and even to the naked eye (if you are standing in a sufficiently dark place). In fact, yesterday I was watching the Orion Nebula with my 4.5" telescope (which is worth $200 or so) from my apartment in the middle of Copenhagen. The term "nebula" is a bit of a… well,...


12

I think my deleted answer to your previous question covers this well, so I'll add it here. These two spots are known as the east and west bays of the Crab Nebula. They appear to be the result of a torus partially encircling a section of the nebula. The pulsar's magnetic field interacts with the gas and dust in the torus, which blocks synchrotron radiation ...


10

The Boomerang Nebula (or Bow Tie Nebula) is a cloud of gas being expelled from a dying low-mass star, at $164~\mathrm{km}~\mathrm{s}^{-1}$ (cf. Raghvendra Sahai and Lars-Åke Nyman: The Boomerang Nebular: The coldes region of the universe?). In general, when a gas expands, it cools (see extended explanation below). If the gas were optically thin to the CMB — ...


10

If you go to this site, http://heritage.stsci.edu/2015/01/supplemental.html , there is a set of comparison photos. The movement that is detectable is very slight but it is there.


10

The answer to your first question is (now) fairly simple: No, brown dwarfs are not more common than red dwarfs. A crude approximation is that stars (which are indeed mostly red dwarfs) outnumber brown dwarfs 4 or 5 to 1; see, for example, the review article by Chabrier et al. (2014). This is supported by extensive surveys done in the 2000s and 2010s, ...


9

Barnard 68 has a surface area of around 10 square arcminutes on the sky and is at an estimated distance of around 160 pc. The volume of space encompassed by a sightline to Barnard 68 is therefore about 1 pc$^{3}$. The the density of stars in the solar neighbourhood (hydrogen burning stars with mass above about 0.1$M_{\odot}$) is about 0.1 pc$^{-3}$. So it ...


9

The size of cosmic dust grains is in general given not by some size, but by a size distribution. The only direct measurements of such a distribution are made on dust collected on plates of satellites, which is of course a very local measurement. When we think that distributions look similar — though not exactly alike — in other locations of the Universe, so ...


9

There are two phases to this problem. In order to accrete into stars, a huge amount of angular momentum must be lost to allow so much mass to gather into a small volume. A second problem is how stars like the Sun end up rotating so slowly, when younger versions of stars similar to the Sun rotate much faster. The solution to the first problem may be solved by ...


9

Just a short answer, and likely others will fill in more details. If there is ionization of some atoms, then generally there is recombination as well - you will have both processes going on, roughly in balance with each other. Typically when an electron recombines with an atom, it does so into some excited state. Then as it drops from that excited state ...


8

Stars are responsible. HII regions$^\dagger$ can refer to several things, but usually I guess one thinks of the volumes around star-forming regions. The more massive a star is, the faster it burns its fuel, and at a higher temperature, meaning that the peak of their spectra are more toward the high frequencies. The most massive stars of a stellar population ...


8

Annes Astronomy News says: Fleming 1 is a planetary nebula that lies about 10,000 light-years away in the constellation of Centaurus, while moving away from us at approximately 28.6 kilometers per second. It is named after the Scottish astronomer Williamina Fleming, who discovered the nebula in 1910. Williamina Paton Stevens Fleming (May 15, 1857 – ...


8

The answer is quite simple: you can also see the other side of the room (or maybe through the fume or haze above your oven) when you create a tasty meal) - even when the space between you and the wall is not empty: it is filled with air. But air is thin enough that you can see through even when it might be thick enough to both, absorbe a bit light and emmit ...


7

With an 8" scope, a filter will very likely give you better results than observing without a filter. Although a filter does block light, the crucial aspect is that a filter increases contrast (by blocking light pollution and extraneous wavelengths of light more than the nebula), thereby allowing you to spot low contrast diffuse nebulae (like IC59 and IC1318) ...


7

There is an article here that describes the visible effects quite well. In essence, within a week or so, it would be comparable in brightness to the moon and therefore visible during the day. Betelgeuse would then start a phase of final, rapid dimming and again reach its current brightness level after possibly three years. After six years, it would be ...


7

The Vela Pulsar (PSR J0835-4510 or PSR B0833-45) is a radio, optical, X-ray- and gamma-emitting pulsar associated with the Vela Supernova Remnant in the constellation of Vela. First line of the Wikipedia entry on the Vela pulsar. It's obviously much more spread out and diffuse than the Crab nebula because it occurred more than 10 times as long ago. Here it ...


7

This is an important question to ask about the initial mass function of objects in the Galaxy - and the final answer hasn't been cast as it is a matter of research. Yet, observational data (e.g. see the mass functions for various clusters in this talk), and simulations in more or less good agreement with that (e.g. here or here), seem to indicate that this ...


6

The answer is that in a pre-supernova star, most of its mass is still in the form of hydrogen and helium. It is only the central core where the primordial H and He has fused to heavier elements. This picture of onion layers is typically what you see in elementary text books. It is completely misleading in a quantitative sense. It schematically represents ...


6

The colorful patterns of gas are caused by excitation of gas atoms, e.g. oxygen, from radiation of a nearby star. You would see the same colors as from a distance, as the light is emitted in almost random directions. But you wouldn't see the same region of nebula shining at the same time as seen from Earth, when excitation is caused by a flash of radiation ...


6

"Nebula" is quite an imprecise word; over the years, it's been applied to everything from interstellar dust clouds to supernova remnants to the birthplaces of stars to even galaxies. Wikipedia separates true nebulae into four categories: H II regions, planetary nebulae, supernova remnants, and dark nebulae. In this case, it might be better to make ...


6

The very first stars to form indeed consisted essentially only of hydrogen and helium. When stars die, they leave behind them more massive atoms, as you say. These heavier elements are too incorporated in newer stars when they form. This results in stars which start out with a lower portion of hydrogen and helium, thus making them somewhat less effective; ...


6

First query: YES there are many bok clusters without foreground stars. For density, That's an unclear field of study, confused with dark matter enigma, and the estimates of frequency of "Boks" perhaps only have about 1-2 degrees of magnitude precision. We can't say that there is less than 1 bok for every 10 stars, we can't say there is more than 1 for ...


Only top voted, non community-wiki answers of a minimum length are eligible