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bio website physics.drexel.edu/~groenera/…
location Philadelphia, PA
age 26
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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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Apr
10
awarded  Nice Answer
Apr
2
revised How to calculate the movement of the object passing near other object in space?
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Mar
31
comment How exactly does 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?
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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
Mar
23
answered Is there a fundamental difference between a small galaxy, and a large star cluster?
Mar
23
comment What must/do astronomers reveal beyond their academic papers?
sufficient to be able to reproduce the result. All of that being said, some papers do actually provide the exact data they use to publish their paper with. I'd imagine that paper within the fields of research which are under the highest levels of scrutiny (climatoloty, medical research, high-profile astronomy projects like Kepler) probably make their own datasets available more often than ones in fields which are not.
Mar
23
comment What must/do astronomers reveal beyond their academic papers?
Unless you're talking about review papers (ones which talk generally about a specific field of astronomy/astrophysics), it is simply not realistic for scientists to report this level of detail in published papers. Usually they will have a methods or samples (or both) section to their paper highlighting the source of their data as well as the analysis/reduction procedure which was done on it. Most likely, they do not make the specific chunk of data they use available simply because it comes from some publicly available database. Providing the coordinates for the region should be ..
Mar
23
comment Are we moving away or towards each other?
Wrong on all accounts. It's dark energy which has anti-gravitational properties. Dark matter gravitates no differently than regular matter does.
Mar
23
awarded  Nice Answer
Mar
16
comment What is the Lyman Alpha forest Used For?
@chris Great comment. I'd encourage you to make this into an answer.
Mar
11
comment Is the universe expanding faster than speed of light?
@draks I don't think that this answers my question to Gerald. Inflation blew up the coordinates of the universe, however, the fact still remains that he has quoted that the distance at which objects are moving faster than c is larger than the distance traveled by light since the big bang.