Travis Thieme

Travis Thieme

I am currently a PhD student at National Tsing Hua University in Taiwan. My main area of research is the birth of stars and planets. I am also passionate about astronomy and physics education.

Location Taiwan

Activity

  • @NeilMcLellan Great Question! I think as presently conceived, since Dark Energy (also known as the cosmological constant here) is a part of space itself the Dark Energy density would remain constant throughout space. There's a figure in the article showing log(Time) vs. log(Energy Density), where the cosmological constant is constant. But, like the article...

  • Hi @GaryE. Technically, wherever you are would look like the "center", as you would have things moving away from you in all directions. The whole universe is expanding and it is doing so equally at all places, as far as we can tell.

  • Hi @NeilMcLellan and @LaurenceScott! I tried to write my own answer earlier but going deep into this requires a lot of explanation. So I found a nice article that talks about some of the points you've mentioned here. I think it explains the whole concept very well and is written by a fellow astrophysicist (usually I wouldn't recommend a Forbes article, but...

  • @GaryE Yes! It's called LISA (Laser Interferometer Space Antenna). It's a future NASA/ESA project.

    https://lisa.nasa.gov/

  • @TanjaEllenSleeuwenhoek This is because bars are properties of spiral galaxies :)

  • Hi @MaryBoole! Maybe think about it like when you blow up a balloon. The balloon is "finite" and it expands into the environment at the rate you blow air into it. The universe is similar in that respect. "Finite" here just means it has an edge. And that edge is always expanding. Is the explanation okay? I can try to explain it differently as well if needed :D

  • Hi @AndrewThompson! Yes, the universe seems to be finite from what we understand. The meaning of "finite" in this sense is that there is a boundary/edge. The whole universe is expanding, meaning the edge is expanding. No stars or galaxies will ever reach the edge because the universe is accelerating, meaning things at the edge move faster than things closer to...

  • Hi @NeilMcLellan! So you are correct that light will be redshifted into the visible part of the spectrum for objects moving away from us. If the object emits light at UV wavelengths or smaller (which it may or may not, there should be some kind of physical process happening for light to be emitted) and is moving away from us, then light from those shorter...

  • Hi @ChristineElson! Let me explain more. Bars are a feature of spiral galaxies, not elliptical galaxies. There are spiral galaxies with and without bars. So although barred spiral galaxies are thought to be older than spirals without bars, they are, as you stated, one of the stages of galaxy evolution that ultimately leads to an elliptical galaxy. Thus,...

  • Hi @JimMuir! Yes you are correct that the LIGO gravitational wave interferometer detected the merger of two black holes due to the detection of the associated gravitational wave. There is quite a problem with determining the exact location. With just two detectors, we can kind of constrain an area but that area is unimaginably large. With more detectors...

  • Hi @CindyBelt! There is 5 times more dark matter than normal matter in the entire universe.

    When I'm talking about the mass calculated from gravitational lensing, that's only the mass of the foreground object, and that is 10 times more than what we expect. Some of that mass includes dark matter, but it also probably includes mass from normal matter we...

  • @NeilMcLellan Glad it's clear! I'm not completely sure how to explain spacetime other than it's just a mathematical model describing the three dimensions of space and one dimension of time. The wave is just a "disturbance" of those dimensions (in a way~). Like when a raindrop hits the middle of a puddle and creates waves on the surface. The ideas are similar...

  • @GaryE Yes! We've detected several instances of gravitational waves from Black Hole - Black Hole mergers, as well as a Black Hole - Neutron Star merger and a Neutron Star - Neutron Star merger!

    Here's a nice graphic from the LIGO collaboration website summarizing the detections found so far (for those interested):...

  • Hi @CindyBelt! Okay let me try to explain in another way. You are right in that he percentage of dark matter in the universe is ~5 times more than normal matter (4.6% * 5 ~ 23%). When Tomo mentions "10 times", he is talking about the gravitational effect these galaxies have on the light due to gravitational lensing. Gravity is a force that is related to the...

  • Hi there! According to Einstein's general theory of relativity, gravity results from the curvature of spacetime. The more massive an object in space, the more curvature it creates. If the massive object is accelerating, then it causes slight changes in the curvature that move away from the object like a wave at the speed of light. Hence the name "gravitational...

  • Yes! "Dark" simply means we just don't exactly know what it is yet.

  • Yes, it's a very interesting question! Dark Energy is only a placeholder name because we don't know what it is. It certainly could be blue bananas for all we know~ Einstein hypothesized that empty space itself could have energy. In his equations of gravity, there was a term he added called the "cosmological constant" to balance with gravity so the universe...

  • Hi there! You are correct. This is something people are constantly studying, so there will be updates to the number over time as our telescopes/observations get better and our mathematical models become more precise. Although, something to remember is that there is always some error involved when trying to match our models to observations.

  • Hi there! Thanks for the question! Just to try to clear things up, the gravitational effect we measure is 10 times more than what we expect from the mass of the lensing source. Therefore, there must be some "missing mass" that we can't see. People originally though the missing mass could be made up of faint normal matter, such as, gas and dust, black holes,...