New answers tagged

4

Regarding the title: Yes. Does this mean that the star started off as a planet? Yes, a star could technically start out as a planet, if it accreted enough mass. However, this is extremely unlikely, since the planet would need to be 80x the mass of Jupiter for it to undergo nucleosynthesis. Stars require hydrogen fusion and earth has little H. Could ...


3

A star does not start off as a planet; you have a large cloud of gas that is collapsing in on itself due to gravity. The majority of the gas goes towards creating the star (more than 99% in the case of our Solar System). However, gravitational collapses can occur several places in the gas cloud, and some of the gas will contribute towards the collapse of far ...


4

Think of when the planet is at the "side" - there's a little bit of light from the planet (ie, reflecting off the planet) shining towards us. Could it be due to that little bit of light - when the planet is behind the star, it no longer reflects towards us? Maybe that's the effect you have in mind?


1

Just to add, while I think Rob Jeffries answer covers it. Now is it expected that in future more stars will be made of more heavy elements or are there causes/laws which prohibit stars forming of e.g. stars made of elements without hydrogen. While this is unlikely to happen because Hydrogen will stick around as the most abundant element for a very ...


3

Globular clusters formed whilst the gas of the proto Milky Way was still approximately spherically distributed. The gas forms a dissipative system that loses energy and collapses (within the first billion years) to a disk whilst conserving angular momentum. Formed stars and clusters are essentially collisionless so the halo stars continue to have a ...


2

The initial stars were made of hydrogen and helium. These enriched the interstellar medium (ISM) with some chemical elements right across the periodic table, when massive primordial stars ended their lives as supernovae. Subsequent generations of stars continue to enrich the ISM, if their lives are short enough. So the general gist of what you suggest is ...


4

The lines show as either peaks above the black body emission (for emission lines) or troughs below the black body emission (for absorption lines). Though stars more often have absorption lines and nebulae emission.


0

What you want to do is use the relation between Mass, Radius, and Density. The proper expression should be $$\rho_c = \frac{M_c}{(4/3) \pi R_c^3}$$ Your three Jeans conditions are $M_c > M_J$, $R_c > R_J$, and $\rho_c > \rho_j$. By using the relation above, you can transform any of the three conditions into one of the others. For example, going ...


6

I think that there isn't a strict answer to this question. However, I believe the answer is that there's a difference between the core of a hydrogen-burning star and the core of a protostar or star-forming, gas cloud. For a hydrogen-burning star, the core, as you say, is the region of the star where fusion is taking place. This is surrounded by the ...


2

You are right; when referring to stars such as the Sun, the core is usually defined as the volume in the centre where fusion is taking place. In the case of larger stars with fusion occurring in multiple layers, the core is still taken to be the area in the middle where nuclear fusion is producing the heaviest elements. With protostars or pre-main-sequence ...


2

There are a variety of scenarios in which a star can emit gases, although that's probably not the best way to think about it. A better way to visualize it is in terms of mass loss rather than gas emission. Inevitably, most or all of a stars mass must eventually go "back to the galaxy in which they are in." https://en.wikipedia.org/wiki/Stellar_mass_loss In ...


6

The slowest reaction rate in the pp chain determines how quickly hydrogen can "burn" in the core of a sun-like star. That rate-determining step is actually the fusion of two protons to form deuterium via the diproton and a weak interaction decay. The fusion of lithium, whereby it fuses with a proton and then splits into two Helium nuclei is actually part of ...


1

NO The differences between a brown dwarf and a low mass star are based upon their mass. A brown dwarf does not have central temperatures and pressures to create energy using hydrogen fusion. The mass is too low to create these conditions. A star by definition is an object where energy is created using hydrogen fusion. This happens when the core temperature/...



Top 50 recent answers are included