StartsWithABang writes: If you want to find where all the young stars in a galaxy are, you look for the densest regions of gas and dust: the locations where new stars and star forming regions are most likely to occur. In the Milky Way, like all spirals, we expect this to be in the galactic plane, along the spiral arms, and in the innermost region of the disk and bulge. When we look in the wavelengths capable of seeing this — and looking for Cepheid variable stars as tracers — we find that our picture is confirmed absolutely everywhere, except the inner galactic disk. For some reason, in the inner 8,000 light years of the Milky Way, we find that it’s almost completely devoid of young stars. This lines up with what we see in the radio wavelengths, but it turned something we thought was well-understood into a surprising puzzle.
StartsWithABang writes: When we look at spiral galaxies, we think of grand arms, star-forming regions and dust lanes lining our perspective. But unlike face-on galaxies, where everything looks the same, galaxies that appear tilted at an angle often appear to have one half far greater in its dust-richness than the other. This was regarded as a mystery for a long time, but the recent Pan-chromatic Hubble Andromeda Treasury (PHAT) survey confirmed the leading picture: that the dust lanes are confined to a narrow, central region of the disk, and the dusty appearance is an optical illusion. It’s a simple result of perspective, that more of the brighter stars are hidden behind the dust from one side than the other.
StartsWithABang writes: Asking where in space the Big Bang happened is like asking where the starting point of Earth’s surface is. There’s no one “point” where it began, unless you’re talking about a point in time. The reality is that, as far as space is concerned, the Big Bang occurred everywhere at once, and we have the evidence to prove it. If the Big Bang were an explosion, we would discover ourselves in a Universe that had a preferred location with different densities surrounding it, but instead we see a Universe that has the same density everywhere. We’d see a Universe that looked different in different directions, yet we see one that’s uniform to better than one part in 10,000 in each direction we look. And we see a Universe that exhibits zero spatial curvature: one that’s indistinguishable from flat. The Big Bang happened everywhere at once. This is how we know it, and this is what it means.
StartsWithABang writes: When it comes to the Universe, you might think that energy really is only limited by rarity: get enough particles accelerated by enough supermassive, super-energetic sources, and it’s only a matter of time (and flux) before you get one that reaches any arbitrary energy threshold. After all, we’ve got no shortage of, say, supermassive black holes at the hearts of active galaxies. And yes, we do find cosmic rays hundreds, thousands or even millions of times the energy that the LHC can achieve. But when we think about the Universe in detail, these cosmic rays aren’t unlimited in their energy, but are rather stopped in their tracks by the most unlikely of sources: the ultra-low-energy cosmic microwave background, left over some 13.8 billion years after the Big Bang.
StartsWithABang writes: If you ask what the zero-point energy of space itself is, you can sum up all of the quantum fluctuations you can that arise in quantum field theory, and arrive at an absurd answer: 120 orders of magnitude greater than the observed. Yet if you assume that there’s an incredible cancellation and you get exactly zero, that removes the one thing our Universe needs to explain its expansion: dark energy. Yet the Universe has matter, radiation, the Hubble horizon and other forms of artificial boundaries in it, and we know that boundaries (like metal plates in electromagnetism) can cut off some of the allowed modes of quantum fluctuations, and lead to a real force: the Casimir effect. Could this same effect – which exists for all the forces, not just electromagnetism – be responsible for dark energy?
StartsWithABang writes: The idea of stopping a meteor headed towards our planet with nothing but a superpowered human being sounds like a physical impossibility. But if you had a powerful enough, strong enough, fast enough human, it could be done, so long as you obeyed the laws of physics and conserved energy and momentum. The speed your human would need to hit the meteor with would be tremendous; there would need to be something special about this human’s atoms to keep them from flying apart; the energy released by the in-air explosion would be catastrophically huge. But it could, in fact, save the city – or the entire planet – that it would have completely annihilated otherwise. Go and learn the physics of how to stop a meteor with one punch.
StartsWithABang writes: In a four-dimensional Universe (3 space and 1 time), it’s easy to get lost. If you take a random walk, the chances of you coming back to your original starting point in a finite number of steps gets lower and lower the more dimensions you have. If all you could do was walk along a sheet of paper – or even better, along the surface of a pipe – you’d have a much greater chance of return than if you had all three spatial dimensions to deal with. There’s an interesting property of mathematics that if you treat all four dimensions as “space” rather than spacetime and you add in the laws of quantum mechanics, then at very short distance scales, the probability of a random walker returning to their original position behaves like they’re in a two dimensional Universe, rather than four. Could this be a way of reducing the quantum gravity problem from a difficult (perhaps unsolvable) 4D case to an easier (and solvable) 2D one?
StartsWithABang writes: If you want to know what types of stars are found all throughout a galaxy, looking at our own simply won’t do: too much of it is obscured by the plane and our position within it. But there’s an even more impressive galaxy – Andromeda – just 2.5 million light years away. And thanks to the power of the Hubble Space Telescope, we’ve not only resolved individual stars within it, we’ve resolved over a hundred million of them. But when we look towards the center versus at the outskirts of the disk, or even into the halo, we find something very, very different: older, redder, fainter and less-evolved stars. Even more spectacularly: beyond them, a rich slew of distant galaxies, visible out to distances exceeding a billion light years.
StartsWithABang writes: When dark energy was discovered, and the expansion of the Universe was shown to be accelerating, there was concurrently another puzzle that received much less attention: the problem of the Great Attractor. Galaxies appear to move due to both the Hubble expansion and the local gravitational field, but the gravity from the galaxies we saw didn’t account for all the motion. There must have been an additional set of masses, revealed only in the 2010s with the identification of the supercluster Laniakea. All the galaxies in our local neighborhood are headed towards it, but are we moving fast enough to overcome the expansive pull of dark energy? The answer looks to be no.
StartsWithABang writes: Today marks the 50th anniversary of the premiere of Star Trek, our first science fiction adventure that promised a positive view of the future, ushered in by technology and humanity’s best traits. In addition to a utopia where maladies like hunger, disease and poverty were eradicated, Star Trek promised a future where technology was widely available and sufficiently advanced to the benefit of all of humanity. While many of these imagined advances in technology have been met or even exceeded already, such as in the field of medical diagnostics and communication, others like warp drive and the Star Trek transporter may never come to fruition. No matter how much your technology advances, you still can’t circumvent the laws of nature.
StartsWithABang writes: If you want to find dark matter directly, your best hope is to gather a tremendous number of nucleons for it to interact with, wait an incredibly long period of time, and devise a device surrounding it capable of detecting even a single potential collision while distinguishing it from any background signals. That was the exact idea behind LUX, the Large Underground Xenon detector. After a 20 month run with more than a third of a ton of liquid Xenon inside, the LUX collaboration has released their final results. Not only did they achieve four times the sensitivity they anticipated, but they didn’t detect a single event. This eliminates most models of WIMP dark matter, including from scenarios like supersymmetry and extra dimensions.
StartsWithABang writes: Less than a decade after the first human was launched into space, astronauts Neil Armstrong, Buzz Aldrin and Michael Collins journeyed from the Earth to the Moon. For the first time, human beings descended down to the lunar surface, opened the hatch, and walked outside. Humanity had departed Earth and set foot onto another world. While Armstrong and Aldrin walked on the surface, collecting now-iconic photos, deploying science instruments and returning hundreds of pounds of lunar samples, Michael Collins orbited overhead, embarking on a missing that no human being had undertaken before. Forty-seven years later, humanity has never had a bigger breakthrough as far as crewed space exploration goes. Relive it all in this incredible video, made exclusively with NASA archival photos.
StartsWithABang writes: On July 20, 1976, the Viking 1 lander touched down onto the Martian surface, followed just a few weeks later by Viking 2. On board both landers were a suite of three experiments designed to look for signs of life. While the Gas Chromatograph-Mass Spectrometer and the Gas Exchange experiment both came back negative, the Labeled Release experiment — where nutrient-rich molecules tagged with radioactive carbon-14 were added to the Martian soil — gave off a positive release of radioactive CO2. Did our first trip to Mars really find life after all?
StartsWithABang writes: When you look at an active, massive star-forming region like the Orion Nebula, you expect to find new stars dominating, blowing off the gas and eventually bringing the episode of star formation to an end. Previous visible light studies of Orion – the closest region to Earth of massive star formation – seemed to indicate exactly this, with star populations dropping off at masses below about 25% that of our Sun. But a new view of this nebula in the infrared, the deepest ever thanks to ESO’s HAWK-I instrument, showed that we had it wrong. In the regions where star formation was most intense, there were more than ten times as many brown dwarfs – or failed stars – than we had thought previously. This could have profound implications for the number of planets formed in a nebula like this, and the next generation of 30-meter-class telescopes should find out.
StartsWithABang writes: If you’re talking to someone across the same room, what the two of you perceive as time and space might match up perfectly, to the limit of what each of you can measure. But if one of you moves quickly relative to the other, if you experience different gravitational fields or spacetime curvatures, or if the space of the Universe between you is expanding, times and distances will cease to line up. This isn’t a flaw of yours in any way, but rather an inevitable feature of special and general relativity. Observers in different locations can never agree on definitions of distance and time, particularly in an expanding Universe. So we invent some alternate definitions for differently scaled types of distance and time: conformal time and comoving distance, to help us understand what’s going on in the Universe.