This Is The One Way The Moon Outshines Our Sun
“Unlike the Sun, the Moon’s surface is made of mostly heavier elements, while the Sun is mostly hydrogen and helium. When cosmic rays (high-energy particles) from throughout the Universe collide with heavy atoms, nuclear recoil causes gamma-ray emission. With no atmosphere or magnetic field, and a lithosphere rich in heavy elements, cosmic rays produce gamma-rays upon impacting the Moon.”
When you view the Moon with your eyes, you’re not seeing it shine so brightly because it’s emitting its own light. Rather, it’s reflecting sunlight on its illuminated phase and reflecting light emitted from Earth (known as “Earthshine”) on the darkened portion. If you look at the Moon in many different wavelengths, from radio to infrared to ultraviolet to X-ray energies, you’ll find that the Sun is much brighter, and the Moon primarily emits light due to reflection.
But in gamma-rays, that entire story changes. The Sun emits virtually no high-energy gamma-rays, with only minor bursts during solar flared. The Moon, on the other hand, emits high-energy gamma-rays constantly; for almost 30 years we know that it outshines the Sun in this particular wavelength range.
It might sound puzzling to you, but there’s a good physics reason for this, and a fun little science fact that everyone should appreciate. Get the story today!
Ask Ethan: Can Gamma-Ray Jets Really Travel Faster Than The Speed Of Light?
“What gives? Is it really possible for gamma-rays to exceed the speed of light and thereby “reverse” time? Is the time reversal just a theoretical claim that allows these hypothetical super-light speed particles to conform with Relativity or is there empirical evidence of this phenomenon?”
Very recently, a paper came out claiming that gamma-ray bursts, and the jets that give them off, can travel faster than the speed of light. If that sounds too fantastic to be true, there’s a reason for that: particles can travel faster than light, but only in a medium, where the speed of light is less than the speed of light in a vacuum. Gamma-ray bursts, when they occur, exhibit a strange property: the signal is mostly a large peak, but when you subtract that peak out, parts of the residual signal are symmetric: if you flip it, part of it going forwards in time is identical to the remainder going backwards in time.
Sound weird? Well, we’re just getting started! Come find out the true story behind this fascinating phenomenon, and what just became our best explanation of what makes it so!
This One Puzzle Brought Physicists From Special To General Relativity
“With an average speed of 47.36 km/s, Mercury moves very slow compared to the speed of light: at 0.0158% the speed of light in a vacuum. However, it moves at this speed relentlessly, every moment of every day of every year of every century. While the effects of Special Relativity might be small on typical experimental timescales, we’ve been watching the planets move for centuries.
Einstein never thought about this; he never thought to calculate the Special Relativistic effects of Mercury’s rapid motion around the Sun, and how that might impact the precession of its perihelion. But another contemporary scientist, Henri Poincaré, decided to do the calculation for himself. When he factored in length contraction and time dilation both, he found that it led to approximately another 7-to-10 arc-seconds of orbital precession per century.“
Special Relativity was easy enough to discover in a certain sense: the Lorentz transformations, Maxwell’s equations, and the Michelson-Morley experiments had been around for decades before Einstein came along. But to go from Special Relativity to General Relativity, incorporating gravitation and the equations governing motion into the same framework, was a herculean effort. However, it was the simple identification and investigation of one puzzle, the orbit of Mercury around the Sun, that brought about Einstein’s new theory of gravity: General Relativity.
What were the key steps, and how did they help revolutionize our view of the Universe? The history is rich and spectacular, and holds a lesson for those on the frontiers of physics today.
Astronomers Debate: How Many Habitable Planets Does Each Sun-Like Star Have?
“We know that there are between 200 billion and 400 billion stars in the Milky Way galaxy. About 20% of those stars are Sun-like, for about 40-to-80 billion Sun-like stars in our galaxy. There are very likely billions of Earth-sized worlds orbiting those stars with the potential for the right conditions to have liquid water on their surfaces and being otherwise Earth-like, but whether that’s 1 or 2 billion or 50 or 100 billion is still unknown. Future planet-finding and exploring missions will need better answers than we presently have today, and that’s all the more reason to keep looking with every tool in our arsenal.”
Most of the time, in science, the quality of our data drives the size of our uncertainties. When we have very little data and it’s only of poor quality, our uncertainties tend to be large; when we have lots of very good data, our uncertainties shrink. NASA’s Kepler mission has provided astronomers with an unprecedented suite of data on exoplanets, revealing thousands of new worlds beyond our Solar System. And yet, despite all it’s found, if you ask the simple question of “how many Earth-like planets orbit a typical Sun-like star,” answers disagree by a factor of 100: from about 1% of stars have them to there’s between 1 and 2 for each and every such star.
What’s the real story? Where do these uncertainties arise, and are they larger than they need to be? Come get the full story (and watch David Kipping’s video at the end) and find out!
One Cosmic Mystery Illuminates Another, As Fast Radio Burst Intercepts A Galactic Halo
“Although scientists have studied [Fast Radio Bursts] intensely since their discovery, their origins remain mysterious. Meanwhile, an estimated 2 trillion galaxies populate our observable Universe. With incredibly large distances for FRBs to traverse, each one risks passing through an intervening galaxy. Giving off multiple pulses of under 40 microseconds apiece, FRB 181112 became the first burst to intercept a galactic halo.”
Where do fast radio bursts come from? Recent studies have demonstrated that they’re associated with host galaxies, but we don’t understand how they work, why some of them repeat, or why the pulse durations are so variable.
What about galactic halos: how much gas is in them? What is the gas temperature, density, magnetization, etc.? These are big questions about galaxies in general that we don’t have a general picture of. If only there were some way to learn more.
How about luck? We got lucky, in November of 2018, when for the first time a fast radio burst passed through a foreground galaxy’s halo. What did we learn? Come get (and see) the full story!
Is The Universe Filled With Black Holes That Shouldn’t Exist?
“What about at the high end of the stellar mass range of black holes? It’s true that pair instability supernovae are real and are indeed a limiting factor, as they don’t produce black holes. However, there’s an entirely separate way to produce black holes that is not particularly well understood at this time: direct collapse.
Whenever you have a large enough collection of mass, whether it’s in the form of a cloud of gas or a star or anywhere in between, there’s a chance that it can form a black hole directly: collapse due to insufficient pressure to hold it up against gravitation. For many years, simulations predicted that black holes should spontaneously arise through this process, but observations failed to see a confirmation. Then, a few years ago, one came in an unlikely place, as the Hubble Space Telescope saw a 25 solar mass star simply “disappear” without a supernova or other cataclysm. The only explanation? Direct collapse.”
As far as our best theories are concerned, the Universe isn’t filled with black holes of all different masses. Instead, the black holes that the Universe forms are inextricably linked to the processes by which the Universe makes the objects that then become black holes. From stars, there’s a theoretical lower limit of about 5 solar masses, and yet we saw a black hole of about 3 solar masses get created. There should be an enormous drop in black hole frequency above about 50 solar masses, but LIGO may be about to challenge that. And even at the highest end, there should be an upper limit to the masses of supermassive black holes, but a few of the ones we’ve found challenge that limit, too.
Does this mean the Universe is filled with black holes that shouldn’t exist? Or does it simply mean that we need superior models? Get the full story today.
This Is What The Milky Way’s Magnetic Field Looks Like
“The Milky Way’s gas, dust, stars and more create fascinating, measurable structures. Subtracting out all the foregrounds yields the cosmic background signal, which possesses tiny temperature imperfections. But the galactic foreground isn’t useless; it’s a map unto itself. All background light gets polarized by these foregrounds, enabling the reconstruction of our galaxy’s magnetic field.”
Have you ever wondered what our galaxy’s magnetic field looks like? As long as we restrict ourselves to looking in the type of light that human eyes can see, the optical portion of the spectrum, we’re extremely limited as far as what we can infer. However, if we move on to data from the microwave portion of the spectrum, and in particular we look at the data that comes from the polarization of background light (and the foreground light directly), we should be able to reconstruct our galaxy’s magnetic fields to the best precision ever. The Planck satellite, in addition to mapping the CMB to better precision than ever before, has enabled us to do exactly that.
Even though there are still some small questions and uncertainties, you won’t want to miss these incredible pictures that showcase just how far we’ve come!
This Is Why We Don’t Shoot Earth’s Garbage Into The Sun
“Considering that the United States alone is storing about 60,000 tons of high-level nuclear waste, it would take approximately 8,600 Soyuz rockets to remove this waste from the Earth. Even if we could reduce the launch failure rate to an unprecedented 0.1%, it would cost approximately a trillion dollars and, with an estimated 9 launch failures to look forward to, would lead to over 60,000 pounds of hazardous waste being randomly redistributed across the Earth.
Unless we’re willing to pay an unprecedented cost and accept the near-certainty of catastrophic environmental pollution, we have to leave the idea of shooting our garbage into the Sun to the realm of science fiction and future hopeful technologies like space elevators. It’s undeniable that we’ve made quite the mess on planet Earth. Now, it’s up to us to figure out our own way out of it.”
As human beings continue to lead the technologically advanced lives we’re presently leading, we’re also producing waste of many different types. Biohazards, dangerous chemicals, nuclear waste and other pollutants must be kept out of drinking water, agricultural regions, the oceans, atmosphere, and away from populated areas. You might wonder why, now that we’re well into the space age, we haven’t considered shooting Earth’s most difficult-to-deal-with garbage into the Sun?
Well, we have considered it, and there are good reasons not to do it. If you’ve ever wondered why, you’ll really enjoy this read.
Starts With A Bang #48 – The Event Horizon Telescope
Earlier this year, 2019, the Event Horizon Telescope collaboration revealed the first image that directly showed the existence of an event horizon around a black hole. This image, constructed from many petabytes of data from telescopes observing the same target, simultaneously, from all across the Earth, provided a breathtaking confirmation of Einstein’s relativity in a realm where it had never been tested before. But that’s just one image of one black hole at one particular moment in time, and there’s so much more to come from the Event Horizon Telescope.
This month, we’re so fortunate to sit down with EHT scientist Sara Issaoun, who takes us through the past, present, and future hopes for the Event Horizon Telescope and how it hopes to answer humanity’s biggest questions about black holes.
(Image credit: APEX, IRAM, G. Narayanan, J. McMahon, JCMT/JAC, S. Hostler, D. Harvey, ESO/C. Malin)
Happy 230th Birthday, Enceladus, Our Solar System’s Greatest Hope For Life Beyond Earth
“It is still a complete unknown whether Earth is the only world in the Solar System to house any form of life: past or present. Venus and Mars may have been Earth-like for a billion years or more, and life could have arisen there early on. Frozen worlds with subsurface oceans, like Enceladus, Europa, Triton or Pluto, are completely different from Earth’s present environment, but have the same raw ingredients that could potentially lead to life as well.
Are water, energy, and the right molecules all we need for life to arise? Finding even the most basic organisms (or even the precursor components of organisms) anyplace else in the Universe would lead to a scientific revolution. A single discovered cell in the geysers of Enceladus would be the most momentous discovery of the 21st century. With the recent demise of Cassini, on the 230th anniversary of Enceladus’ discovery, the possibility of finding the incredible compels us to go back. May we be bold enough to make it so.”
On this date in 1789, William Herschel, armed with the most powerful telescope known to humanity at the time (you can get a lot of grant money when you discover the planet Uranus and name it after the King), discovered a relatively small moon of Saturn just 500 kilometers across: Enceladus. For some 200 years, Enceladus was never seen as more than a single pixel across, until the Voyager probes flew by it. What they revealed was a remarkable, unique world in all the Solar System. Now that the Cassini mission is complete, we can look back at all we know about this world, and all the signs point to a remarkable story: there’s a subsurface ocean, possibly suitable as a home for undersea life.
Is Enceladus truly our Solar System’s best hope for life beyond Earth? That’s debatable, but there’s every reason to be hopeful. Come get the story here.