“All the evidence, experimental and even a little theoretical, seems to indicate that it is the energy content which is involved in gravitation, and therefore, since matter and antimatter both represent positive energies, gravitation makes no distinction.” -Richard Feynman
It was a big last week at Starts With A Bang, and you might not realize it but next week is shaping up to be even bigger! If you missed anything, here’s what we took a look at:
- How do black hole jets carve out bubbles in space? (for Ask Ethan),
- Beyond human vision, distant galaxy clusters emit spectacular fireworks (for Mostly Mute Monday),
- What your birthstone means, according to science,
- The Milky Way’s most recent supernova was hidden, until now,
- A nearby, infant star teaches us how planets begin to form, and
- How fast does Earth move through the Universe?
That’s quite a collection, but there’s more! For those of you who love podcasts, thanks to our Patreon supporters (some of you included!) I’m pleased to share with you our sixth podcast: on the most distant galaxy (so far) in the Universe!
From Alan L. on dark matter and whether it’s displaced by normal matter: “‘the idea that dark matter is displaced by normal matter runs counter to the evidence that dark matter appears where normal matter does.’
Except, apparently, in the vicinity of the world’s ever expanding collection of increasingly sensitive dark matter detectors.”
The dark matter detectors you refer to — all of them — rely on three very specific assumptions:
- That dark matter has a substantially non-zero interaction cross-section with normal matter through either the weak or electromagnetic interactions,
- That dark matter is of a particular variety and a particular mass,
- And that the combination of the cross-section and scattering amplitude means we’ll have an event rate above the background of neutrinos, neutrons, cosmic rays and so on.
The fact that there’s a null result from all such detectors designed in this way likely tells us that whatever the cross-section of dark matter is, it’s below what these detectors can detect. It may indicate that dark matter isn’t the class of matter these detectors are looking for. The idea that dark matter is displaced by normal matter has no evidence for it, and is just another “let’s make an unmotivated assumption with no way to test it” (i.e., a bad idea) that we can’t rule out. It’s important to keep it in mind, but keep it waaaaay in the back of your mind, where it belongs.
From Denier on global warming and El Niño: “You seriously believe the El Niño conditions only contributed 0.1° C? Seriously?!?”
Well, yes, in the sense that one “believes” the conclusions that scientists who are experts in the field draw. According to the best reconstructions I’ve seen, the figure is 0.07 +/- 0.03° C, with the warming effects only really impacting the September/October temperatures and onwards. But that’s me “parroting” what the actual scientists said, and I consulted a number of those scientists when I wrote my article in the first place. They signed off on it and told me I had it correct, but if you doubt their scruples and their work, then your doubt will trickle down to my writings as well. According to NASA’s GISS, the mean influence of El Niño is 0.09° C for the 2015 year (within the errors of aggregate estimates), but based on how El Niño worked in 1983, 1987/8, and 1997/8, we can expect the El Niño contribution to be sustained and larger for the present year: 2016.
From Omega Centauri, dissatisfied with spherical heating from linear jets: “That was unsatisfying. The gas responds primarily because it get heated, and one would expect the heating would need to be spherically symmetric in order for the “explosion” to be spherically symmetric. Now I think it should be intuitively obvious that the jet will simply blast through the gas, so whatever else happens we have holes punched out by the jets. Then the problem becomes one of explaining why the rest of the energy is deposited in the gas in a roughly spherical manner.”
I want to show you a different simulation: one of a supernova conflagration event beginning from an off-axis point in the core.
Which is what we see in the X-ray and gamma-ray part of the spectrum, even around our own Milky Way!
That’s because there is a big difference between “Kepler’s supernova” above, which occurred in 1604 and was attributed to Johannes Kepler, the day’s top astronomer, and the supernova that Kepler (the spacecraft) spotted in its field of view.
We’ve never seen an initial flash like this, but what’s worth noting is that it gets an additional ~8 times brighter than this flash gets it to, which tells us that supernovae are practically instantaneous for the nuclear explosion, but when it comes to the light, they aren’t these instantaneous processes we think of. Pretty interesting!
From Michael Kelsey on the discovery and new measurement of the protoplanetary disk around TW Hydrae: “In addition to the ESO version (10 Mar 2016), the “as submitted” paper from 30 Mar 2016 is up on arXiv, http://arxiv.org/abs/1603.09352“
The biggest takeaway from the paper — and anyone who wants to read it, it’s free and complete in the link Michael provided — is not that there’s an “Earth-like” planet in there, as many people have (erroneously) reported. The big thing you want to look for is gaps and empty spaces in the dusty disk around the star. In addition to the ones I’ve highlighted (which may be planets, planetesimals or merely illusive phantasms), there’s pretty good evidence for a number of features at ~6, 13, 23, 38 and 43 A.U., in addition to a definite lack of dust altogether below 1 A.U.
The empty spot may indicate a planet or many planets; it may indicate a rocky planet or a series of rocky planets or a series of super-Earths or a mix of rockies and super-Earths (but not gas giants; they would show up on their own). But the coolest thing that we learn from this is that planet-containing inner Solar Systems are common even from the earliest times! Now, it’s time to get to higher-resolution on this so we can find more of them farther away, and figure out what’s happening in here!
See Noevo on how fast Earth moves through the Universe: “I guess the answer is: many different speeds.From
The earth’s speed
– orbiting the sun,
– revolving in our galaxy,
– moving in the local groups,
– and inflating into a bigger universe.
What is our speed for the last?”
By “inflating into a bigger Universe” you clearly mean relative to the rest-frame of the cosmological expansion, which you clarified in a later comment. What’s odd about asking this is that every question you asked is answered in the article. But in case you missed it:
- 30 km/s,
- 220 km/s,
- our Milky Way moves towards Andromeda (relatively) at 300 km/s,
- our local group moves through space at a total of ~627 km/s,
- and we move, all total, relative to the CMB at ~368 km/s.
And finally, one more from our buddy See Noevo in the general category of misunderstood things about the Universe: “I understand that the *FLRW metric* assumes the universe is *isotropic.* If that’s so, it doesn’t make sense to me, because, obviously, the universe *does* look *different depending on where you are in the universe*.”
Yes, the FLRW metric does assume the Universe is isotropic.
No, isotropic does not mean “the Universe looks the same from all locations.” That’s what “homogeneous” means, which the FLRW metric also requires. Isotropic means the same in all directions.
But the Universe does not look different on large scales depending either on where you are or what direction you look in. The large-scale density contrast is tiny, on the order of ~0.003%.
The Universe does look different when you look back in time, but that is because of — wait for it — the fact that the Universe has only been around for a finite amount of time, and because given enough time and physical laws, physical systems evolve. So, See Noevo, i.e., see no evolution, I understand that you come at this from an ignorant viewpoint: without the knowledge to decide what’s correct and what’s incorrect. I (and many other commenters here, including Michael, whom you wrongly deride) am providing you with that information that you’re seeking, and it gives you the information you need to make those determinations for yourself. You can stick to your guns, but if you do, you move from the point of view of ignorance to one that has only ever been accurately described by the wise words of Dale Gribble.
Do better than that. You know you can, I know you can, and everyone here knows you can. Come on; it’s time to take the years of information you’ve been provided, put them together and solve this puzzle for yourself.
Thanks for a great week, everyone, and I’ll see you back here tomorrow, where we’ll kick off with a spectacular exclusive: an interview with the executive director of LIGO!