3,484 reputation
526
bio website physics.drexel.edu/~groenera/…
location Philadelphia, PA
age 26
visits member for 11 months
seen 22 hours ago

I'm a Ph.D. candidate in the field of Physics at Drexel University. My research interests include the formation and structure of dark matter in galaxy clusters and gravitational lensing.


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22h
reviewed Leave Closed What is the secret behind the existence of gravitational force?
Jul
24
comment Could dark matter particles be unstable?
@Envite That is absolutely incorrect. Astronomer's do not define dark matter as cold gas, dust, or the like, which is simply unobservable.
Jul
24
comment Did we ever actually see the earth revolving around the sun? Is the geocentric model completely disproved?
Well, epi-cycles were introduced to correct for the retrograde motions of the plants in a geocentric model; they never really worked super well, and even if one could make them work mathematically, they represent really complicating and unphysical orbits... Not the best argument, but I thought it should be included here.
Jul
24
awarded  Custodian
Jul
2
awarded  Curious
May
26
revised Calculating Angular Distance
azimuthal coordinates is more appropriate
May
18
answered How to calculate right ascension of Greenwich?
Apr
10
awarded  Nice Answer
Apr
2
revised How to calculate the movement of the object passing near other object in space?
deleted 19 characters in body
Mar
31
comment How exactly does inflation convert random gravity fluctuations into coherent gravitational waves?
I don't think the title of this question makes much sense. Inflation doesn't cause gravitational waves, inflation blows them up to macroscopic scales.
Mar
26
comment Is there a fundamental difference between a small galaxy, and a large star cluster?
... to find objects of this mass unassociated with galaxies or clusters. I don't know this for sure of course, but my intuition tells me that if it is able to be flung out of the galaxy entirely, chances are it has been disturbed in the process. It is hard for me to imagine a situation where a globular cluster could be flung out of a galaxy and remain the size and shape it was to begin with. If any have been found, please update this post!
Mar
26
comment Is there a fundamental difference between a small galaxy, and a large star cluster?
@called2voyage I'm not entirely sure what you mean by mechanism - if you mean gravity, then yes, these types of objects do attract dark matter from their host galaxies/clusters in the form a gravitational wake (en.wikipedia.org/wiki/Dynamical_friction) - this is the cause of some dynamical friction of, say, a star cluster orbiting around the center of a massive galaxy. The question remains though: Do these objects contain some known radial distribution of dark matter intrinsically, or is the dark matter present simply from the parent object? I think you'd be hard pressed...
Mar
26
comment Is there a fundamental difference between a small galaxy, and a large star cluster?
@Jeremy In practice I don't think people go looking for dark matter in these star clusters/globular clusters. Lensing is not really something I've seen be used to determine total mass of these objects (I don't think the geometry works out for these objects), but one could use the velocity dispersion to infer total mass. But no, I do not think an assessment of dark matter is made in order for people to say if an object is truly a star cluster or a galaxy. You could be right about people using stellar population age and gas content to make this type of statement - I simply do not know.
Mar
26
comment Is there a fundamental difference between a small galaxy, and a large star cluster?
... it all came from. Since DM doesn't interact electromagnetically, it was able to cool off and form overdensities for which baryons would later fall into - basically, the baryons do trace the dark matter. For a sufficiently massive dark matter overdensity, it is able to collect enough gas for there to be a galaxy within; for smaller overdensities, there may not be enough gas within to form a galaxy, and to that end, there may not be enough to even form any stars. This is the idea behind dark companion galaxies, and has been proposed as a solution to the 'missing halo problem'.
Mar
26
comment Is there a fundamental difference between a small galaxy, and a large star cluster?
@eraticus Well, whether total mass is an absolute distinction which can be made to determine an object's classification is not something I couldn't say is universally true. Stars are a different case - they are discrete packages of gas which at one point either collapsed due to an overdensity in a region or did not because it simply didn't have enough mass (I know there are other effects here that determine star fomation; from a purely Newtonian perspective, I think my statement is not unreasonable). When it comes to the formation of galaxies and galaxy-type objects, you have to remember where
Mar
24
comment Why isn't the dark energy getting decreased?
No - Dark energy is the cause of the acceleration of the universe. There are other combinations of $\Omega_{i}$ which cause the universe to expand and contract which do not contain dark energy.
Mar
24
comment Do the E and B modes of the CMB polarization have anything to do with electric and magnetic fields?
OK - the details are added. Let me know if any further clarification is needed.
Mar
24
revised Do the E and B modes of the CMB polarization have anything to do with electric and magnetic fields?
added 1064 characters in body
Mar
23
answered Do the E and B modes of the CMB polarization have anything to do with electric and magnetic fields?
Mar
23
revised Is there a fundamental difference between a small galaxy, and a large star cluster?
added 354 characters in body