Hot answers tagged

18

S0-2 (I assume you mean the star orbiting the Milky Way central black hole) actually reaches speeds of 7650 km/s at periapsis. However, if you read further down the wikipedia article you will see that there are stars S0-102 and S62 which have shorter orbital periods than S0-2 (11.5 and 9.2 years vs 16.05 years). Star S62 is also in a highly elliptical orbit (...


12

There are a couple of stars with smaller orbits (and hence faster average speeds) S55 and S62. Of these, S62 has a faster speed at periapsis, approximately 10% of the speed of light: the orbital time scale is measured to be 9.9 years, the next peri-center passage will be around March 2023. During that passage, the star will have a velocity of about 10% the ...


6

HD 51684 is a magnetic Ap star. It has an entry in the recent catalogue of fundamental parameters for magnetic stars by Glagolevskij (2019). This catalogue lists it as having $T_{\rm eff}=7800$ K, and a mass of $2.3 M_\odot$. These parameters are determined from the photometric properties of the star - i.e. they are not fundamental measurements of the ...


5

Very roughly. The star is in hydrostatic equilibrium so $$ \frac{dP}{dr} = -\rho g$$. Replacing $dP/dr$ by $P_c/R$, where $P_c$ is the central pressure and $R$ the radius, and letting $\rho \propto M/R^3$ and $g \propto M/R^2$, then we get $$ P_c\propto \frac{M^2}{R^4}$$ But the central pressure is proportional to $\rho T/\mu$, where $T$ is the interior ...


4

For massive stars and their remnants, one can only be guided by theoretical measurements at present, since we do not have any masses for isolated neutron stars and black holes and no measurements of the masses of the progenitors of any neutron stars or black holes (only limits). Here are two plots taken from the extensive review by Limongi (2017). These show ...


4

A query to the Gaia Archive within 6 arc min of target name M51 finds 20 sources with phot_g_mean_mag <= 17. Aladin Lite helps to locate them visually. Five are circled in the lower half of the image in question: Gaia source_id ra ° dec ° parallax (mas) magg 1551894661845524736 202.4034 47.1522 8.854 ± 0.017 14.3 1551988532650838016 202.4205 47.1790 2....


3

Simbad gives a parallax of 4.0452 mas, which is equivalaent to 1/0.0040452 parsecs. That is 247 parsecs or 805 light years (but the error bars on that are quite high, 0.59 mas ie from 700 to 940 light years) It is listed as in spectral class F0, which means up to about 1.5 times the mass of the sun. It is also listed as a double star, so this refers to ...


3

The dynamics of the Solar System and the chemistry of the Solar System bodies don't support a hypothesis of a stellar merger later than formation of the protoplanetary disk which would have mixed-up things considerably and heavily disrupt any circumstellar disk. Thus this basically excludes any collision after the time one can start talking about a protostar,...


3

Higher mass stars will have shorter lives. Even though they have more fuel for nucleosynthesis, they burn this fuel much quicker than lower mass stars. Generally, you should think of "red-giant" as an evolutionary phase and not a particular type of star. Looking at the Scheller et al. (Aston. Astrophys. Suppl., 96, 269, 1992) data given in one of ...


3

You might want to have a look into a stellar structure and evolution book for this, such as Kippenhahn. But in short, for a star such as the sun the following happens: Throughout the lifetime, H is slowly being converted to He in the core. This changes the mean-molecular weight $\mu$ of the core with time. The hydrostatic law demands for the stellar ...


2

A catalogue is just that what one would understand usually: it's a table of stars with their coordinates and possibly other properties like relative or absolute brightness, proper motion etc. The accuracy depends on how it was created, thus mostly is expression of the available instrumentation, processing pipeline and its limitations. They usually are output ...


2

Don't have high enough reputation to comment, but someone should mention the Stefan-Boltzmann Law: https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law When a planet (or anything) gets warmer, the amount of radiation it emits increases with the 4th power of temperature (measured on an absolute scale like Kelvins). A planet's temperature reaches ...


2

I like sharing the following quote from Wikipedia on the Star of Bethlehem Astronomers have made several attempts to link the star to unusual celestial events, such as a conjunction of Jupiter and Saturn or Jupiter and Venus, a comet, or a supernova. Some modern scholars do not consider the story to be describing a historical event but a pious fiction ...


2

Guide9 from projectpluto.com will do this. You choose Chart mode (Display, Background, Chart mode). Right clicking on a star or any other object will give you the information you want. It runs on all versions of Windows. It is not freeware, and is a bit dated in some aspects.


1

Stellar mergers are certainly possible, but also relatively rare. Maybe protostars merging is a bit more common since they have less relative velocity. However, unless the merger is straight it will typically deposit a lot of angular momentum. The sun seems to be a slow rotator for its spectral class. Hence it is not likely it was formed through a stellar ...


1

When the initial conditions, like mass, chemical composition, and rotation are the same, for the vast majority of stars there are no intrinsic variations in their development. Of course, statistical variations exist, like convection. But those act on too small scales in order to influence the star’s development, in particular its core. Intrinsic large scale ...


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