Thursday
Jun132013

How far away is that pulsar, exactly?

A team of scientists just used a Hemisphere-sized network of radio telescopes to find out exactly (well, within 0.4%) how far away the binary pulsar J2222-0137 is. With this new distance, which is 15% closer than everybody thought it was, astronomers can figure out what the pulsar's orbiting companion is and are one step closer to detecting gravitational waves.

Spoiler alert: This pulsar is 871.4 light-years from Earth.

But it's not the actual distance that matters. The important part is that astronomers can figure out the distance at all. Here's the story in three acts.

Act 1: PulsarsThis is not an image (Credit: Bill Saxton/NRAO/AUI).

They're weird.

Aside from black holes, they're the weirdest things in the universe. They have more mass than the Sun but are the sizes of earthly cities. In other words, dense. According to a Nature Physics result released today, they are made of nuclear pasta. They spin tens or hundreds of times every second (seriously, imagine DC rotating 716 times in a "one Mississippi," as the fastest known pulsar does) and warp spacetime way more than you do. Once every time they spin, the radiation coming out of their poles is pointed toward Earth, so we see a pulse.

Most pulsars are precise "clocks," hardly slowing down at all. If a pulsar is spinning once per second today, you can bet the farm that it will be spinning once per second tomorrow. As long as the person you're betting against doesn't have a super-atomic stopwatch. The average pulsar will slow down by approximately 10-15 seconds every second, which means that a pulsar that spins every 1 second today will spin once every 0.999999999136 seconds tomorrow. 

But the fast-spinning pulsars -- called millisecond pulsars (MSPs) -- are even more precise. If one rotated every 0.01 second, that number might change to 0.00999999999999136 seconds tomorrow.

These minute changes in period, too, are stable.

Act 2: Pulsars as tools

Because pulsars appear to pulse once for each rotation AND their rotation changes so slowly and measurably, astronomers know when they should see each pulse.

For the fastest and most stable objects, one could almost say they know exactly when they should see each pulse. So when one is off by 0.0000001 second, a dozing graduate student (j/k) sits up and takes notice.Bow down, atomic clocks. You have been beaten. By tiny, dead stars. (Credit: METAS).

Astronomers who are part of the European Pulsar Timing Array (EPTA), the Parkes Pulsar Timing Array (PPTA), and North American Nanohertz Observatory for Gravitational Waves (NANOGrav) are searching for -- you guessed it -- gravitational waves (GWs).

GWs ripple spacetime when objects with mass interact, like when they orbit each other or collide. As a GW passes through the universe, undulating the fabric of the cosmos, it will affect pulsars' pulses. Astronomers, obsessively monitoring a batch of the most reliable pulsars, are watching for tiny deviations in their pulses' arrival times, incidcating they were delayed by GWs. The set of pulsars -- currently there are 40 -pulsars that are worthy -- that astronomers watch closely is called a "pulsar timing array." Having more pulsars and knowing more about each one -- say, its distance from Earth -- increases the array's abilities.

Although scientists have found indirect evidence that gravitational waves are real and not something Einstein just made up, no one has seen them directly. Pulsar-timing astronomers would like to be the first. 

Act 3: Binary pulsar J222-0137

In the research paper headed-up by A. T. Deller of ASTRON, the scientists share new details about J222-0137, which is in a binary system that the Green Bank Telescope (GBT) discovered as part of a large survey.

Objects orbiting around each other radiate gravitational waves into space. They don't look like this unless you squint and turn your head to the right (Credit: NASA).

It

  • is 871.4 light-years away
  • spins every 32.82 milliseconds, or 30.5 times every second
  • will spin 0.00000000000000409536 seconds slower tomorrow
  • has a binary companion that is at least 1.1 times as massive as the Sun. Its nature is still unknown, but since astronomers know its mass and its distance, ID is on the way. If it shows up in optical observations, it's likely a white dwarf. If not, it's likely a fraternal twin neutron star.

They did all of this with precise observations from the National Radio Astronomy Observatory's Very Long Baseline Array, a set of 10 radio telescopes that work together to synthesize a larger radio telescope that has higher resolution than Hubble. By measuring the pulsar's parallax*, or how much it appears to move relative to distant background objects, they made the most accurate distance measurement ever for this kind of object.

Gathering up lots of accurate distance measurements to the timing-array pulsars would help in the race to finally "see" gravitational waves. Unfortunately, the paper says, most of the superfast pulsars are much farther away than J222-0137, and their parallaxes would be harder -- or, for the most part, impossible -- to measure well.

But fear not. Science, like love, will find a way ... to find gravitational waves.

It will, however, take a lot longer if the National Science Foundation (NSF) de-funds both the telescope that discovered this pulsar (and at least 85 of its closest pulsar friends) -- the GBT --- and the VLBA. Both are under threat of divestment, meaning all NSF funding would disappear.

Not good for many science topics, but especially for GW research. Maura McLaughlin, a professor at West Virginia University and an author on this paper, says, "Both the GBT and the VLBA are absolutely essential to detecting gravitational waves with pulsars. The GBT is the most sensitive instrument in the world for pulsar searches, and the VLBA can measure pulsar distances more accurately than any other telescope. Accurate distances to pulsars dramatically increase our ability to characterize gravitational wave sources. The GBT and the VLBA are really a perfect match, and it would be disastrous if we lost one or, god forbid, both of them."

ResearchBlogging.orgDeller, A., Boyles, J., Lorimer, D., Kaspi, V., McLaughlin, M., Ransom, S., Stairs, I., & Stovall, K. (2013). VLBI ASTROMETRY OF PSR J2222-0137: A PULSAR DISTANCE MEASURED TO 0.4% ACCURACY The Astrophysical Journal, 770 (2) DOI: 10.1088/0004-637X/770/2/145

 

 

**I've written about parallax several times. If you're interested in this technique's superpowers, consider these posts:

  1. For a summary of why parallax is important, see "Wink once if you think astronomy is is better because of parallax."
  2. VLBA-observed parallax bested Hubble's distance estimates and solved a mystery.
  3. Parallax also proved the most famous black hole actually is a black hole and not something else weird.
  4. To read an overview of the different ways scientists determine how far away stuff in space is, check out the intro of "Variable Stars: Blinking the way to better distances since 1957."
Wednesday
May292013

A new microbe that correlates with weight loss

by Brooke Napier

Meet the bacterium Akkermansia muciniphila. It’s new to me too. I’m scared but excited.

All I remember about Belgium is the chocolate waffles, sweet beautiful waffles.

Patrice Cani and her team at the Walloon Excellence in Life sciences and BIOtechnology (WELBIO) Institute in Belgium isolated Akkermansia muciniphila from the mucus layer of the intestine. They were particularly interested in this mucus dwelling bacterium because they found the presence of it interferes with the permeability of the intestinal layer.

Why is the permeability of the intestinal layer important?

Recently this same group found that increased permeability of the intestinal layer is associated with obesity and type 2 diabetes. They found this by showing that obese patients or patients diagnosed with type 2 diabetes showed signs of bacterial lipids (specifically endotoxin lipopolysaccharide) within the blood.

How would bacterial lipids get into the blood? Permeability of the intestinal wall.

The presence of these bacterial lipids cause chronic inflammation of the intestine, which is horrible for anyone to live with (but comes in handy when you know this type of person because they always know where the bathroom is…) and this inflammation is a hallmark of obesity and type 2 diabetes.

See that circle? It’s a beautiful scientific circle, but it’s a dreadful real-life circle. What is missing is what is causing the intestinal permeability, and that is where Akkermansia mucinphila comes in…

This is not the first group to have the idea that our gut microbiota is responsible for intestinal permeability in this scheme, however they are the first to identify one out of millions of bacterial species that correlates with this symptom, and that’s pretty huge.

Akkermansia mucinphila is a mucin-degrading bacterium that resides in the mucus layer of the intestine. It loves the mucus layer so much that is the predominate species found in this wet, sticky, dark layer – and interestingly the presence of this bacterium inversely correlates with body weight in humans (and mice!). Meaning, genetically and diet-induced obese mice had a dramatic decrease in A. mucinphila.

How is Akkermansia mucinphila related to weight loss/gain and type 2 diabetes?

It turns out, the presence of A. mucinphila in the intestines restores intestinal permeability in diet-induced obese mice, or type 2 diabetic mice. They did this by having control mice, high-fat diet mice, and another set of control + A. mucinphila (Akk) and high-fat diet + mucinphila (below).

M = mucus layer, IM = inner mucus layer

Basically, A. mucinphila decreased intestinal permeability, bacterial lipids in the blood, insulin resistance, and chronic inflammation AND increased mucus layer thickness (above) and adipose tissue (FAT!) degradation – all in obese or type 2 diabetes model mice. All of this without changing any of the other gut microbiota.

Miracle bug? Perhaps.

Basically I want this bug in me. Interestingly, there is a prebiotic that increases colonization of the gut with A. mucinphila called oligofructose, however the mechanism is uses to increase this gut microbe is unknown (along with it’s side effects in humans). So maybe just a pill with A. mucinphila within a capsule (that can withstand the low pH of the stomach)?  Would that even work? I’m not sure, but…

I would sign up for that study.

 

 

ResearchBlogging.org Everard, A., Belzer, C., Geurts, L., Ouwerkerk, J., Druart, C., Bindels, L., Guiot, Y., Derrien, M., Muccioli, G., Delzenne, N., de Vos, W., & Cani, P. (2013). Cross-talk between Akkermansia muciniphila and intestinal epithelium controls diet-induced obesity Proceedings of the National Academy of Sciences, 110 (22), 9066-9071 DOI: 10.1073/pnas.1219451110

Tuesday
May212013

SS Cygni: A red dwarf-white dwarf pair that's closer than scientists thought (or, how Hubble got told)

Determining distances to objects in space is no easy task, unless you're some kind of special person with an impossible faster-than-light spaceship and can just measure the miles between Earth and UDFj-39546284. This is what it's like to be in a helicopter above SS Cygni, minus the arrows and text (Credit: J. Miller-Jones [ICRAR], using software created by R. Hynes).But no astronomer I know has such a ship, and so they all are likely to say, "That galaxy is 3 billion light-years away, plus or minus a million light-years."

And that level of uncertainty doesn't apply only to far-away objects. It also applies to relatively nearby stars, such as SS Cygni, a close binary system in which a red dwarf and a white dwarf orbit each other every 6.6 hours. The Hubble Space Telescope had pegged the distance between us and SS Cygni at 540 light-years.

And, well, it's not often that you get to tell the Hubble Space Telescope it's wrong. But when the Hubble Space Telescope is wrong, you gotsta tell it loud and clear. So, "Hubble, SS Cygni is more like 372 light-years away. Take that in your face."

And what instruments were able to so diss the high-res space telescope? The Very Long Baseline Array (VLBA), a combination of 10 radio antennas spread between Hawaii and St. Croix, giving the telescope as a whole an effective diameter of more than 5,000 miles, and the European VLBI Network (EVN), which has antennas in Europe, China, Russia, and South Africa.

Here's the low-down on the SS Cygni system, how scientists used the VLBA to determine its distance from us, and why that 168 light-year revision matters.

What is this binary system like?

The solar flare in the upper left extends 100,000 miles from the Sun's surface, the same distance as the separate between SS Cygni's two stellar components.

Tight. The red and white dwarfs are separated by only 100,000ish miles. If the Sun were that close to another star, the star would begin just at the end of the solar flare in the image to the right.

Such a close sharing of quarters can lead to violent outbursts on the part of the white dwarf. The white dwarf roommate siphons material--Ramen noodles, the last of the Fruity Pebbles, clean underwear--from the red dwarf roommate, and all that stuff forms a disk around the white dwarf. When the white dwarf is taking a lot of material, the relationship is stable (and the analogy totally unravels), but when the transfer rate is lower, the disk destabilizes and undergoes an outburst. 

This burst happens with regularity--in the case of SS Cygni, once every 49ish days. Because of these explosions, it is categorized as a dwarf nova. It's only during the burst period that the system emits radio waves. 

But it didn't appear to work the same way all the other dwarf novae do.

This is what astronomers thought until today: SS Cygni is too bright. It's so bright that lots of mass must be changing hands. So much mass that the disk should always be stable. Meaning SS Cygni should never, ever have an outburst. But it does--often. If SS Cygni is in fact 500 light-years away, and is super bright but does the nova thing anyway, our theories about how dwarf novae work must be wrong.

So when amateur astronomers from the American Association of Variable Star Observers (AAVSO) noticed that it was, in fact, having an outburst, they informed professional astronomers, who perked up and took action because they were eager to prove that their theories were not, in fact, wrong.

When an object emits radio waves, and you have a 5,000-mile diameter radio telescope, you can do science. 

Who are these so called "professional astronomers," and what did they do with that gigantic telescope?

A team led by James Miller-Jones from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) took advantage of the radio emission to watch how it "wobbled" compared to the galaxies behind it (from our perspective).

"The wobble we were detecting is the equivalent of trying to see someone stand up in New York from as far as away as Sydney," Miller-Jones said in a press release.

Why couldn't astronomers do that any old time using the optical light, even if it's not emitting radio waves?

After all, SS Cygni is always putting out visible light.

"Our key advantage was using radio telescopes to observe the system. In visible light, optical telescopes like Hubble see hundreds of different stars, all of which are moving by different amounts, whereas in radio waves the background we compare against is much further away and therefore doesn't appear to move at all," co-author Assistant Professor Gregory Sivakoff from the University of Alberta, said.

Energetic radio galaxies were much more common at the beginning of the universe, so most are extremely far away.

Why are far-off things better for determining distance?

Astronomers were trying to find SS Cygni's parallax, which is the numerical measurement of the "wobble"--how much it appears to move relative to a distant background when the observer's position changes.

When you're looking out the passenger window of a car, the road's shoulder is flying by you, but the mountain peak moves slowly across your view. If we can measure the angle by which an object appears to move due to our motion, we can determine how far away it is--this is parallax.Parallax is based on the concept that objects close to you seem to "move" faster when you're moving than far-away objects do. I'm about to plagiarize myself here, but I'm being honest about it. "When you're looking out the passenger window of a car, the road's shoulder is flying by you, but the mountain peak moves slowly across your view." Because of that differential, astronomers can measure the difference between how the "shoulder"and the "mountain peak" change relative to each other and thus determine how far away the "shoulder" is.

Wikipedia user Natejunk2004, aka Best Screen-Named Person Ever, made this animation demonstrating what I clumsily tried to convey above.

Miller-Jones, et al., looked at SS Cygni when Earth was at different, widely separated points in its orbit (see the figure to the left) and observed where it was relative to background radio galaxies from each of those perspectives. The radio galaxies, by the way, are so distant that they don't seem to move at all.

So they used parallax to figure out that SS Cygni is 168 light-years closer than they'd previously thought. So what?

Well, if SS Cygni is closer to us, it's not quite as intrinsically bright as scientists thought. It's just nearby (in the same way that the Sun seems to be really bright compared to Sirius but is really just average and next-door). Which means that the mass transfer rate is low enough to create an unstable disk. Which means that astronomers were right about dwarf novae (or, at least, that they weren't wrong in this particular way).

And we all know how astronomers love to be right. Right?

But, really, using evidence to prove that a physical process does mesh with a theory is truly a significant scientific feat. It is, in fact, what science is all about.

 

 

Monday
May062013

How to see a black hole birth

by Sarah Scoles

 

What if this was what you did to the space around you? How would you feel? Well, scientists can't answer that, but they now may be able to tell when a black hole is forming. even if its stellar progenitor doesn't explode (Credit: Alain Riazuelo, IAP/UPMC/CNRS).

When really massive stars die, they collapse into black holes. But no one has actually observed this process in action. So what happens, exactly, when a star stops being a star and starts being the universe's weirdest object? How does it look, and what signals would allow scientists to point at some tiny spot in the sky and say, "Hey, right there, a black hole was just born"?

A new paper suggests one such signal, and, almost as importantly, this paper has a great title: "Taking the 'Un' out of 'Unnovae.'" Good job, sole author theoretical astrophysics postdoctoral researcher Anthony L. Piro.

Piro suggests that the death of a star and the subsequent birth of a black hole--the Simba-style circle of cosmic life--is marked by a specific type of flash.

Wait, did you just use the word 'unnova' and proceed to write another sentence before defining it?

Sorry. While some stars-turning-black-holes produce spectacular explosions that are supernovae or supernova-like and/or include ultra-energetic gamma-ray bursts, others may simply implode and disappear without all the fanfare. This "now it's there, now it's not" version is the theoretical-and-as-yet-unobserved unnova. As in, not a nova.

But it is something, even if it is not a nova. When a massive star is turning into a black hole, it collapses into a neutron star first, its protons and electrons so squished together that they combine into neutrons. As the star is essentially cramming itself into a medium-sized city's limits, it is also releasing neutrinos--nearly massless particles that travel almost as fast as light and don't interact much with the rest of the universe. As a result, the star loses about a tenth of its mass in the course of a few seconds.

Consider losing a tenth of your mass. Like you would, the star feels its loss of gravitational strength. While you would probably just run faster or jump higher or be really hungry, the star can no longer hold on to its outer layers. As they expand, they create a shock wave in the star's envelope, which is consequently ejected. When the wave reaches the star's surface, the surface heats up and glows. It's a bit like a slow-mo, low-energy supernova...which is not a supernova at all and is, in fact, an unnova. The resulting light, though it would last for about a year, is too faint for our telescopes to reliably identify at the moment.

Piro's paper asks the question, "Is there a brighter signature within the unnova-ing process that scientists could latch onto?"

The short answer: Yes! A flash.

The longer answer: When the shock wave hits the star's surface, he predicts there will be a blast of light. Not nearly as bright as a supernova, but 10-100 (I know, I know, check out that range) times brighter than the "glow."

In other words, if scientists can find instances of this flash, which Piro estimates should occur detectably once per year, they will be able to say, "Look at that unnova! Probably," and will suspect that they have seen a black hole being born. And who doesn't want to be in the delivery room to witness that?

All of a sudden, this emerges from the dying massive star, and everybody's like, "What?" (Credit: DC Comics).

Stats on the flash:

  • it would last 3-10 days (so "flash" is perhaps not the best word to describe it, except to astronomers, who think on million-year timescales at the smallest)
  • it would equate to a temperature of 10,000 kelvin, or 17,540F
  • it would travel at a max speed of 200 km/second or 124 miles/second
  • it wouldn't show any evidence of nuclear synthesis, but hydrogen would be prevalent
  • it would have a luminosity of 10^40-41 ergs/second, or 2.6 million-26 million times as bright as the Sun
  • it would be brightest in UV light but a similarly strong blue component

So keep your transient-identifying, world-class UV-sensitive telescope's eyes open, and maybe you'll be the first one to see a black hole progenitor's final moments, before it Houdinis itself out of the visible universe.

ResearchBlogging.org Piro, A. (2013). TAKING THE “UN” OUT OF “UNNOVAE” The Astrophysical Journal, 768 (1) DOI: 10.1088/2041-8205/768/1/L14

Wednesday
May012013

Learning: What’s programmed cell-death proteins got to do with it?

by Brooke Napier

A. Healthy Cell :) B. Apoptotic Cell :(Apoptosis is programmed cell death. It is controlled cellular suicide that is responsible for humans not having webbed fingers.  Less dramatically this time - apoptosis effectively and efficiently removes extra and unnecessary cells during development.

Cellular proteins called caspases control apoptosis. Caspases are a family of proteins known as cysteine proteases and they mediate cell suicide by forming protein complexes with activating complexes in the presence of adaptor proteins. They cleave other caspases and other cellular substrates to orchestrate a very controlled cellular destruction.

Humans encode 11 caspases, and while most of them dedicate their folded-life to carrying out apoptosis, some caspases have been known to dabble in immune regulation (ex: containing inflammation during infection to the site of infection) and spermatogenesis (you’ll have to ask a sperm-centric Ph.D. candidate about this one).

Mouse interdigits in utero - red cells are apoptotic. Fingers, ya'll!Although I have previously emphasized the importance of apoptosis/caspases in the development of our digits (I <3 my thumbs), ANTI-apoptotic molecules (members of the BCL-2 family) are extremely important during the development of the brain. There is relatively little turnover in the brain, so maintenance of differentiated neurons (peripheral neurons specifically) is very important.

Since apoptosis is specifically down-regulated in many neurons, one would assume that after development of the human brain caspase proteins are no longer needed in a healthy human. But then why have so many researchers found that caspases are required normal, everyday neural functions?

Caspases are serving a completely different function in the healthy adult human brain.

Ah ha! It turns out caspases can also dabble in other, very important neuronal functions. In fact there is data showing that activation of caspases in neurons can control normal neural physiology.

What are the new roles for caspases in neural physiology?

Ye ole dendrite. Gorgeous as ever.

1) Dendritic pruning, or trimming the hedges, if you will. Dendrites (from the word tree in Greek) are beautifully branched neurons that transmit electrochemical stimulation from other neural cells to the soma, or cell body, of the dendrite, which then makes the executive decision to pass on the electrochemical signals to more dendrites via neurochemical synapses. This is the beautiful orchestra that is neuron-to-neuron communication in the nervous system.

Pruning of the dendrites is important for normal brain functions, it removes neglected or misguided dendritic branches, which would normally get in the way of forming fresh, new, sparkly synapses. Just like learning, the formation of our neural connections are fluid, and caspases grease the spokes.  This mechanism of plasticity is as important as it sounds; Caspase 3 has been implicated in the zebra finch and fly models of learning and memory.

2) Axon guidance and synaptogenesis. Basically if you make a mouse that is caspase-deficient you have successfully made a mouse that has defects in axon targeting and synapase formation during development, which leads to significant developmental delays.

After poking my nose into this research, it seems like not a lot is understood about how caspases effect axon guidance or synapse generation – but there is preliminary data that suggests without some specific caspases axons show delayed/misguided maturation and some proteins required for synapse generation are impaired.

3) Normal synaptic physiology, turns out low levels of caspase 3 activation are required for synaptic changes that underlie memory.

Related, long-term depression (LTD), where synapses become less sensitive to stimulus (and the dendritic branches shrink or get eliminated), is associated with local activation of Caspase 3. Turns out, if you block caspase 3 or 9 activation you can effectively stop LTD! Follow the Figure legend below to learn more about this mechanism.

Too bad we can prescribe caspase 3 inhibitors for patients diagnosed with LTD (remember all the other things caspases do?).

The once infamous rapid-cell-death associated family of proteins has now relinquished its former title and should now be referred to as: Caspases: the we-can-help-you-learn family of proteins. In the words of Bradley Hyman and Junying Yuan:

“In addition to being a signal of acute, inexorable death, caspase activation in other circumstances (at least within the CNS) might instead be a pivotal event for responding to ever-changing environmental stimuli.”


ResearchBlogging.org Hyman, B., & Yuan, J. (2012). Apoptotic and non-apoptotic roles of caspases in neuronal physiology and pathophysiology Nature Reviews Neuroscience, 13 (6), 395-406 DOI: 10.1038/nrn3228