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Ethan Siegel
Works at NASA's The Space Place
Attended University of Florida College of Liberal Arts and Sciences
Lived in Bronx, New York
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Ethan Siegel

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“When the clusters collide, their mutual gravity causes an incredibly energetic cosmic smash-up, heating the gas to such high temperatures they emit X-rays. Mysteriously, on the outskirts of the collision, intense radio emission can be found. The fact that these two signals are offset indicate that there's another, secondary process at work.”

When two galaxy clusters collide, there are a slew of cosmic certainties you can bet on: all the galaxies will miss one another, the intracluster gases will collide and heat up, and X-rays will be emitted. But on rare occasion, radio emission can be found, too. Which is a puzzle, since that requires electrons to gain an extra factor of 1,000,000 in energy! How can that happen? Up until recently, it was a mystery, but a new colliding cluster, Abell 3411 and 3412, has shown something incredible: gas shocks on the outskirts of the X-ray collisions appear to get a blast from nearby, active supermassive black holes, giving the electrons the needed boost and creating those energetic electrons after all!

Go get the full story in pictures, videos and no more than 200 words on today’s Mostly Mute Monday!
The X-rays are powerful and reveal the matter, but the radio emission requires energies a million times greater. How does the collision do it?
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Matthew Rapaport's profile photo
 
Good column, and very good one on the "why no dark matter black holes" subject.. 
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Ethan Siegel

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“And so this camera has taught us a lot about how stars die. But what it’s also told us about is how and where they’re born! You see, these nebulae don’t just dissipate after a few thousand years; they often spit out entire star systems worth of gas, and trigger the formation of new stars. One of the most spectacular pictures took place deep inside the Eagle Nebula.

And when Hubble imaged the pillars at the center of it, it was one of the most amazing things ever.”

Over its more than 25 year lifetime, the Hubble Space Telescope has shown us what the Universe truly looks like. It’s done so in a myriad of ways, from planets to stars – dying and forming – to galaxies to gravity’s effects to the deepest abysses of blackness of all. Nothing in space is the same as it was before humanity knew Hubble. Yet even the camera most responsible for our iconic images, WFPC2, isn’t the end of the story. That camera was removed in 2009, and in the 8 years since, we’ve deepened our views and our understanding even further. Even before the launch of the James Webb Space Telescope, our journey into the unknown Universe continues with Hubble in a way we never could have imagined when the observatory was first launched.

Come see for yourself in far more images than you’ve ever seen at once before!
More than 25 years since its launch, it hasn't stopped amazing us.
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Ethan Siegel

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"At its core, science is two simultaneous things, neither one of which is valuable without the other: a full suite of knowledge and data relevant to a particular issue, and a process for testing, inquiring, refining and reproducing our best explanations for that full suite of information. Being aware of the enterprise of science means having a tremendous respect for the people devoting their lives to furthering our understanding of any aspect of the Universe in this fashion, from the instrument builders to the experiment conductors to the data analysts to the theorists working to create an overarching framework. Being aware of the enterprise of science means recognizing your own inability to be competent in all areas of science no matter how smart or qualified you are; it means recognizing the need for legitimate expertise and for valuing the conclusions thereby reached."

Are you scientifically literate? Do you even know what that means? You'll periodically see quizzes designed to assess some measure of science literacy, and they'll usually focus on a slew of general knowledge questions, inevitably decrying what a large fraction of people don't know. But is that a fair assessment of scientific literacy, or what it means to be scientifically literate? Highly doubtful. At its core, scientific literacy isn't about being able to answer questions about science correctly or to explain various phenomena, but about two things that most people generally don't think about: having an awareness for what the enterprise of science is and having an appreciation for what scientific knowledge and discoveries do for humanity.

If you think both of those things describe you, or you'd like them to, come find out what that really means and entails, and learn what it truly means to be scientifically literate.
Are you scientifically literate? Find out!
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Matthew Rapaport's profile photoRandall Lee Reetz's profile photo
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Self assessment seems a suspiciously unscientific test of science understanding or "litteracy".
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“But there’s another, green line that happens only when oxygen gets doubly ionized at the hottest temperatures of all: 50,000 K and above. Only planetary nebulae, with super-hot young white dwarfs, and the ultra-rare “green pea” galaxies exhibit these features. But by looking at the most active star-forming galaxies in the Subaru Deep Field (above), Matthew Malkan and Daniel Cohen found, that all galaxies from 11 billion years ago or more emit this green signature.”

Galaxies come in many different colors today: white, blue or red, mostly, depending on the populations of stars inside. But in a very rare set of circumstances, there can be green emissions as well, due mostly to the emission lines of doubly-ionized oxygen. The problem is we only see these in extraordinarily hot regions of the Universe, where ultra-hot stars or extremely unusual ultraviolet processes are found. Yet by looking at the farthest star-forming galaxies available, two scientists broke the light up into components and found something shocking: this green emission feature was found to be incredibly strong in every one of thousands of galaxies that fit the criteria. It leads to a huge mystery: how do these ultra-hot stars form in the first place? Is it metallicity? Higher stellar masses? Or a top-heavy initial mass function?

The jury’s still out, but it’s looking more-and-more like these are the galaxies that reionized the Universe in the first place! Come get the whole story on this week’s Mostly Mute Monday!
The stars that power them shouldn't be this hot, but the colors don't lie.
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“The Universe may have began from a singularity, where time and space emerged from a state where there was no time and space outside of it (as much as concepts as “emerged” or “outside” make sense with no space or time), but it also may have come from an ultimately non-singular state. However, as long as we have the second law of thermodynamics, which means as long as the overall entropy of a system can never decrease, the “big bounce” ideas have a very large obstacle to overcome.”

If you take a look at our Universe today, you can learn all sorts of things about it. How the matter in it is distributed, what the radiation is doing, how many and what types of black holes we’ve formed, how much entropy there is, etc. You can also learn how all of those things are evolving into the future and how they were different in the past! And if we go all the way back, we find that in General Relativity, we expect to wind up at a singularity at some point in the beginning. In a quantum formulation of gravity, that isn’t necessarily true! There are four classes of ways to avoid a singularity in the beginning, where space and time always exist, rather than having a creation or emergence. But many of the four have serious, fundamental issues that may yet make them impossible.

Go beyond our observations and into the realm of the theoretical “beginning of everything” on this week’s Ask Ethan!
Can we rule it out based on entropy considerations alone?
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Ethan Siegel's profile photoMatthew Rapaport's profile photo
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P.S. you are also assuming inflation which itself is controversial as you know.
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“For the first time, we can now study the distribution of elements across our galaxy. The elements we measure include the atoms that make up 97% of the mass of the human body.”

If you want to know how many and what type of chemical elements are present in a star system, you need to make a dizzying, intricate array of observations. You need to break up the light from the star into its component wavelengths and look for the signatures of absorption and emission lines corresponding to each individual element you’re seeking, while simultaneously accounting for effects like temperature and ionization. This is made extra difficult by the fact that most of the Milky Way is obscured by gas, dust and other neutral matter. But thanks to the infrared instruments on the wide-field Sloan Digital Sky Survey, over 150,000 stars have had their spectra taken, located throughout the Milky Way, and the results are spectacular. In particular, the center of our galaxy has more heavy elements than we do, potentially meaning that it could have begun harboring life billions of years earlier.

The elements of life are everywhere, but they’re not equally distributed at all locations. And therefore, Star Wars could be real!
If the ingredients are everywhere, perhaps life is thriving in places we can only imagine.
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Excellent article, but I'm afraid I read the whole thing with Brian Cox's accent in my head. 
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Ethan Siegel

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"“When you get right down to it, this is just more elitism.”

Yes. Yes, you said it, and this is right. Elite, expert knowledge — someone armed with expert facts, expert skills, expert reasoning and the ability to draw expert conclusions — is worth more than the opinion of a non-elite person. There is no greater example of this than in science. [...] Will you, without that expertise, follow the arguments and teachings of experts and adhere to what they conclude? Can you do it? Will I see you do it here? And will I see you do it as respects all aspects of robust, well-understood science even if it’s not well-understood by you?"

There are a slew of things to follow-up on this week, from mysteriously green galaxies to exploding stars to the Big Bounce and entropy to the origin of the heaviest elements in the Universe and much more. But the biggest thought-provoker was on the topic of scientific literacy. It's not something you can measure with a test, at least, not if you want to do it right. Rather, you can only measure it with humility: how willing you are to admit that you yourself are not the expert you need to be to evaluate a scientific claim. For that, you need a real, legitimate scientist in that field.

Are you willing to go there? Find out on this edition of our comments of the week!
“Men go abroad to wonder at the heights of mountains, at the huge waves of the sea, at the long courses of the rivers, at the vast compass of the ocean, at the circular motions of the stars, and they pass by themselves without wondering.” -Saint Augustine Well, another week has gone by — the…
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Wouldn't the "early metal poor stars" be much larger than present stars, metal poor or not? Wouldn't that size cause them to be hotter?
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"As it stands today, we know the Hubble expansion rate better than we ever have, and yet our two different method of arriving at it seem to give irreconcilable values. There are a myriad of different measurements going on right now attempting to find out which camp is right, which camp is wrong, and exactly where the errors lie. If history has taught us anything, we can say for certain that two things will come of this: we're going to learn something additional and wonderful about the nature of our Universe when this gets resolved, and that this current controversy won't be the last one concerning how the Universe expands."

It seems like the simplest, most fundamental quantitative question about the expanding Universe of all: how fast is it expanding? Even though it's been more than 80 years since Hubble's most career-defining discovery, we still don't know the answer. In fact, the two main methods we have of measuring it give incompatible results. The largest-scale observations, like the cosmic microwave background and baryon acoustic oscillations, give a result that's on the low side: 67 km/s/Mpc. On the other hand, distance ladder measurements, relying on individual stars, galaxies and supernovae, give a higher result: 74 km/s/Mpc. But these are known well enough that they're inconsistent with one another.

This is a story that's been ongoing since we first learned the Universe was expanding, but the next five years should be critical in resolving this tension. Find out why!
Over 80 years since the expanding Universe was discovered, the debate still rages.
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Mark Ruhland's profile photoJames Carlson's profile photoJack Martinelli's profile photo
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the subtleties of expansion are quite difficult to grasp in the context of ordinary measurements of length and time. I made a video that explores this subject :

youtube.com - Dark Energy Solved


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"By the same token, the James Webb Space Telescope will teach us an incredible amount about the Universe, including further details about how stars form, what the earliest stellar populations look like, will show us gas giants and rogue planets in unprecedented detail and will tell us what made up the Universe at any given time in the past. It will show us a whole slew of things that Hubble cannot, by virtue of it reaching to much longer wavelengths of light than Hubble could ever hope to see. And with its huge, large-aperture primary mirror, it will be able to collect more light in a single day than Hubble could in a week. The most exciting things, of course, will be the unexpected: the things we'll discover that we don't even know to look for yet.

But even if you don't learn about any of the science that James Webb will bring to us, there's one thing it will deliver that everyone can enjoy: the James Webb Space Telescope will show us how the Universe grew up."

The Hubble Space Telescope, for all of its scientific findings and how it revolutionized our understanding of the Universe itself, touched us all in a way that no piece of knowledge could ever encapsulate. In perhaps the greatest find of all, Hubble answered a question that many of us have had on our minds every time we've gazed up at a night sky: what does the Universe actually look like? From its images of star-forming regions, stellar deaths, galaxies, gravitational lenses and the deep abyss of empty space, it's awed us in a way no other observatory ever has. But James Webb is poised to do us one better, and show us something Hubble never could. It will show us how the Universe went from a state with no stars, no planets, and no galaxies to the Universe we know, recognize and inhabit today.

In short, the James Webb Space Telescope will show us how the Universe grew up. Come learn exactly what that means, and see if you aren't awed by the possibility!
Launching next year, humanity's most powerful telescope of all time will reveal the answers to questions we've always dreamed of.
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CheapPhilosophy's profile photoMatthew Rapaport's profile photo
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I'm awed by the possibility but this bird isn't flying yet! Let's keep our collective fingers crossed that it does.
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“Yes, it’s like a World Wrestling Entertainment fight. Someone villainous actor can club the truth over the back of the head with a folding chair, but when the scrupulous hero goes to pick up the folding chair, the referee notices. The hero gets disqualified. And suddenly the villain is victorious. This is what I object to. This is what I resent. You may not see this happening but I do, and many others do as well. Not just with something where there isn’t a nefarious actor like the EmDrive, but when there’s over fraud involved. You may object to the “make a law” route, and claim it’s unconstitutional, and I don’t enough know about such matters to evaluate that one way or the other; I have to defer to someone with more expertise. So then the challenge is this: how do we change the way business-as-usual is done to value the correct information of a valid expert over the gain-motivated misinformation of a fraudster?”

There has been an incredible roundup of scientific news from this year’s annual AAS meeting, and we’ve taken on an entire slew of amazing stories. I may be in the airport, unable to upload images, edit articles or post links very well, but we’re doing our damnedest to deliver the best stories plus our weekly dose of bonus science to you. Don’t miss it on this special edition of our Comments of the Week!
“Life would be tragic if it weren’t funny.” -Stephen Hawking Well, the first week of the year is behind us here at Starts With A Bang! For most people, that means struggling to return from a long holiday break, but in the world of astronomy that means we’ve just come back from an incredible week of science…
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Mark Ruhland's profile photoMark van Walraven's profile photo
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I was a bit surprised when I read Dr Hossenfelder's blog post; I'm glad to have heard your perspective on it.
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"Black holes don't just provide gravity, absorb incoming matter and prevent anything from escaping. They also gravitationally pull on and tear matter that passes nearby, including stars. In a surprising find, a new study out of Harvard shows that torn-apart stars aren't merely reduced into gas, but they form dense streams that re-condense into planets in just year-long timescales. Moving rapidly away from the central black hole, these 'cosmic spitballs' represent a brand new population of rogue planets, and are potentially the most catastrophic objects from space careening through our galaxy."

Imagine you’re a star passing too close to a black hole. What’s going to happen to you? Yes, you’ll be tidally disrupted and eventually torn apart. Some of the matter will be swallowed, some will wind up in an accretion disk, and some will be accelerated and ejected entirely. But quite surprisingly, the ejected matter doesn’t just come out in the form of hot gas, but it condenses into large numbers of rapidly-moving planets. This population should make up approximately one out of every 1000 rogue planets, but should be uniquely identifiable. The vast majority will move at incredible speeds of around 10,000 km/s, be approximately the mass of Jupiter but will be made out of shredded star material, rather than traditional planetary material. As the next generation of infrared telescopes come online, these ‘cosmic spitballs’ should be one of the most exciting novel discoveries of all.

Come get the whole story on cosmic spitballs, fresh from the AAS meeting!
A new theoretical study shows it isn't just gas and radiation, but catastrophic 'spitballs' that get sent out from black holes.
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David Carlson's profile photo
 
Ah ha! Finally, slim circumstantial evidence that self-gravitating objects smaller than a Jeans mass are ejected from a larger Jeans mass, i.e. ejected from a star, which weighs against the standard theory of cometary knot (CK) formation in planetary nebulae by Rayleigh Taylor instability of gas streaming away from the degenerate white-dwarf core.

Alternatively, CKs are ejected from the late stage of AGB stars (just prior to the planetary nebulae phase) by super-intense magnetic reconnection, as a kind of super-intense coronal mass ejection.
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"From a physics perspective, it's long been assumed that the fundamental constants and the laws of nature really are the same everywhere and at all times. However, one particular dimensionless constant, α, the ratio between the electric charge, the speed of light and the Planck constant, has been shown by a number of previous studies to show variations both the farther back in time we look and at different locations on the sky. However, new observations by a team working at Arecibo observatory, of the quasar PKS 1413+135, have placed a very tight constraint on the time variations, casting doubt on the previous findings. To only 1.3 parts in a million, the fundamental constant α once again appears to be truly constant."

We assume that the fundamental constants are truly constant, but they don't have to be. The speed of light is the same everywhere, but it could have been different elsewhere, either in space or in time. The same is true for other constants, like Planck's constant, the gravitational constant, or even the fundamental charges or masses of particles. You might not think it's likely, but the evidence indicated otherwise. Over the past 20 years, time variations and spatial variations in the fine structure constant, which determines the force of the electromagnetic coupling, have been observed to about 5 parts in a million in different locations and at different distances. It was a disputed but intriguing finding, but new evidence was just released conflicting with those results. Instead, the fundamental constant, α, once again appears to be truly constant, to better than 1.3 parts in a million, thanks to the new results from Arecibo.

There's always more work to be done, but one of the greatest puzzling results from the astrophysical community might not be a puzzle after all!
Even over billions and billions of years, the laws of physics were exactly the same.
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They are constant NOW but perhaps evolved into there present values in the opening femto seconds of the big bang. Reached present values at time of nucleo synthesis. Then on the other end, trillions of years from now they may evolve into different values.
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Theoretical Astrophysicist / Writer / Educator
Employment
  • NASA's The Space Place
    Columnist, 2013 - present
  • Trap!t
    Head Editor: Science/Health, 2011 - present
  • Starts With A Bang!
    Science Writer, 2008 - present
  • Lewis & Clark College
    Visiting Assistant Professor of Physics, 2009 - 2011
  • University of Portland
    Professor/Lab Coordinator, 2008 - 2009
  • Steward Observatory/University of Arizona
    Postdoctoral Research Associate, 2007 - 2008
  • University of Wisconsin
    Faculty Assistant, 2006 - 2007
  • University of Florida
    Teaching/Research Assistant, Fellow, 2001 - 2006
  • King/Drew Medical Magnet High School
    Teacher, 2000 - 2001
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Bronx, New York - Yonkers, New York - Evanston, Illinois - Torrance, California - Gainesville, Florida - Madison, Wisconsin - Tucson, Arizona - Portland, Oregon - Houston, Texas - Rome, Italy
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Science writer, professor and theoretical astrophysicist
Introduction
Theoretical Astrophysicist, Science Writer and Communicator, expert in (some aspects of) dark matter and dark energy, physical cosmology, and sometimes professor, teacher and educator.

Creator and writer of Starts With A Bang!, the 2010 Physics Blog of the Year! Author of over 1,000 articles, featured in Esquire, the St. Petersburg Times, ESPN.com's Page 2, and many others.

Competitive beardsman and amateur acrobat / halloween-costumer extraordinaire.
Education
  • University of Florida College of Liberal Arts and Sciences
    Physics, 2001 - 2006
  • Northwestern University
    Physics, Classics, Integrated Science Program, 1996 - 2000
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