“The black holes in these early [galaxy] clusters are like piranha in a very well-fed aquarium,” said Jason Eastman of the Ohio State University and first author of this study.

While there are some feeding supermassive black holes (technically called Active Galactic Nuclei or AGN) in the modern universe, they are rare. Using the Chandra X-ray Observatory, Eastman’s team found that when the universe was 8 billion years old there were 20 times more AGN than there were when it was 11.2 billion years old. Today, the universe is 13.7 billion years old and there are no nearby AGN.

In the early universe, galaxies were rich in dust and gas that could be used to form stars or to feed AGN. When the AGN gobble the dust and gas, they often burp out high-energy jets and expel blasts of X-rays that stifle star formation, leaving galaxies devoid of stellar nurseries.

Fighters, take your corners. At the bell, publishing round one will end.

[Bing]

In a paper submitted to the astronomy pre-print server on June 8, 2007 Tanmay Vachaspati of Case Western Reserve University argues that black holes don’t exist. This statement is based on the relativistic statement that time for objects (particles count) trying to form a black hole slows to the point that the objects appear to hover seemingly forever just outside the forming black hole’s event horizon. Thus, argues Vachapati, the black hole never actually forms.

Here is what happens: You have a giant star, on order of 10 solar masses in size or larger, and it stops generating light for some reason. When light stops pushing the outer layers of the star apart, the star begins to collapse. Initially, inter-particle forces try and prevent things from crushing too closely together, but they lose, and gravity crushes the atoms together causing explosive nuclear reactions. These nuclear reactions fire the outer layers of the star out as a supernova, but the inner regions just continue to crunch together, and the protons and electrons and neutrons are all crushed together until they lose their individual identities. Somewhere inside this infalling mess is a point at which the pull of the mass inside that radius is so strong that not even light is going fast enough to escape (on Earth anything going faster than 11.2 km/s can escape. The speed of light is 300,000 km/s). As the infalling material accelerates toward this point of no return it goes faster and faster. As it goes faster, its time goes slower compared to clocks on a not infalling Earth (this oddly means the object actually appears to slow down). Eventually, when an observer feels like they are going their fastest - a hairsbreadth slower than the speed of light perhaps - they appear, to us, to stop. Thus, a black hole, never quite finishes collapsing down to that mythical singularity as viewed by an external observer.

BUT… we see black holes doing things like merging, and eating things, and acting like fully formed black holes.

In the greatest stretch of semantics I have seen since I last graded exams, Vachaspati uses this failure of black holes to finish forming in the reference frame of the observer to argue that the objects merging aren’t black holes, but something he names black stars. He then talks about how when these non-black hole objects collide the particles can explosively collide and give off *observable* gamma ray bursts.

BUT… (in steps Petrovay), the same factors that cause the black holes to not finish forming in our reference frame also prevent two merging objects from physically touching in our reference frame. This in turn prevents them from giving off gamma ray bursts, as Vachaspati argues above. And even if they could physically collide, and they did emit gamma rays, that light would be gravitationally redshifted - the gravity of the system would pull on the light and suck energy out of it causing it to appear redder and redder. Petrovay actually says “it would be gravitationally redshifted+dilated into oblivion.”
In effect, from the perspective of the objects forming black holes, the suckers fully form, fully collide, and much violence occurs. From our perspective, they never actually finish forming. They act like fully formed objects, because time systematically slows for everything getting too close, making that stuff disappear as though it had fallen into a fully formed, mushed to a singularity, black hole. If it acts like a black hole (by not releasing light), smells like a black hole (by not releasing smells), and in every way is as sweet as a black hole (in a 1990’s ‘Swe-eet, dude’ kind of way), it is a black hole. You can call it a black star, but please don’t try and change its physics. You will just be wrong.

The judges’ scores for round one are in, and this round goes to relativity and its Hungarian physics fighter, K. Petrovay.

One interesting note about these papers is that at the end of Vachaspati’s “black hole’s are black stars” paper, he thanks several people for their input, including Martin Rees (and I’m assuming he means Sir Martin Rees, the Nobel Laureate). He also says that his work was supported by the US Department of Energy and NASA. On first reading, it could be assumed that Sir Rees gave positive feedback on this work and that funding was granted specifically to explore the possibility that Black Holes don’t exist. Now, that could be true. However, what he wrote could just as honestly be written if he had grants to pay for other research and this is a footnote to that other research program (sorta like if you get money to study Saturn’s rings and a really cool star does something really neat while it is in the same field of view as Saturn’s rings - you are purposely studying the rings, but something totally unrelated results). What he wrote could also honestly be written if Rees pointed out some problems and he added in a sentence to address each of these problems without getting Rees to give a second round of commentary to tell him if the problems were actually addressed. It is just impossible to know. I don’t think attempts were made to mislead, I just have trouble believing that Rees would have approved of this paper for publication (and in fact this isn’t a published peer reviewed paper - it is just a paper put into to public record).

Okay, rubber necking time is over. Move along. Good new science is waiting to be discovered.

That was a lot of exciting information, and now that I’ve gotten some of the excitement out of my system, let me step back and tell you exactly what it means.

At time T = 0, the universe formed. Poof, we have the the Big Bang rumbles the universe into existence.

Over the course of almost 400 millennia, the universe evolved from pure energy, to atomic nuclei, to full atoms with electrons. At that last, wonderful, electron grabbing moment, at T + 372,000 years the Cosmic Microwave Background came into existence.

And then the universe went dark. If you have ever looked at an image of a dark molecular cloud, you have seen what the entire universe looked like after the electrons and nuclei got together to form neutral hydrogen and helium (with a bit of lithium and beryllium). There was nothing generating light, and astronomers refer to this time as the cosmic dark ages.

Then, at some time we are still determining, the first stars turned on, and as they heated the gas around them the universe began to glow. Have you seen images of star forming proplyds in the dense gas of the Orion nebula? This is what the early universe may have looked like, as the hot stars heated and ionized the neutral gas. We call this the epoch of re-ionization.

As of today, we know the epoch of re-ionization occurred no later than T+500,000,000 years.

Astronomers Daniel P. Stark, Richard S. Ellis, Johan Richard, Jean-Paul Kneib, Graham P. Smith, and Michael R. Santos used the Hubble Space Telescope and Keck II to discover these galaxies using gravitational lensing. (There is a neat collection of lead up paers here and this work occurs in the July 1 Astrophysical Journal.) Every distribution of mass has specific regions where objects appearing in those regions may be extraordinarily magnified by gravitational lensing. This team identified the regions of greatest potential gravitational lensing around 3 different galaxy clusters and looked specifically in those regions for extremely high redshifted objects. Specifically, they looked for the atomic line Lyman alpha that is strong in star forming galaxies. This line is created by electrons in hydrogen transitioning from the lowest energy shell (n=1) to the second lowest (n=2) energy shell. Normally, this line has an ultra-violet wavelength of 121.6 nanometers. The expansion of the universe, however, causes this line to get doppler shifted to the red. In the case of these extremely distant galaxies (z=8.5-10.4), the Lyman alpha line is shifted all the way to the infrared wavelength band, and appears between 1143 - 1375 nanometers.

To find this specific atomic transition, they performed spectroscopy with NIRSPEC on the 10m Keck II telescope with the slit of the spectroscope aligned along the line of maximum gravitational lensing in a cluster. Over 1 hour of telescope time went into every final spectra, and 2-5 different final spectra were obtained for each of 9 clusters. All told, 35 different telescope pointing were used and roughly 0.3 square arcminutes of sky — about the size of a decent but small crater on the moon — was observed. In this small area of sky, 6 low luminosity galaxies (fainter than Andromeda would be at the same distance) were discovered in 3 different clusters (Abell 68, Abell 1689, and Abell 2219).

Follow-up images and spectra were obtained with the Hubble Space Telescope and Keck II to confirm these were real results. “As with all work at the frontiers, skeptics may wish to see further proof that the objects we are detecting with Keck are really so distant,” confessed Ellis. However, in addition to numerous checks the team has made(described in their published scientific article, which gives 5-8 sigma confidence), there are also images of galaxies from when the universe was only a billion years old that show extremely old stellar populations. Those stars would have had to have formed at extremely high redshifts.

While 6 galaxies may not seem like a huge number, finding this many galaxies in so small an area indicates that if there is an even distribution of these systems, then there are enough of them to light up the universe and end the dark ages. So, for those of you afraid of the dark, avoid times T+373,000 to T+~500,000,000, and you’ll always have light from space to light your way.

In the coming years, planned telescopes such as the James Webb Space Telescope, and earth bound behemoths like the CalTech 30 meter will have the capabilities of seeing systems like these without relying on gravitational lenses to boost the light we can see. With in the next couple decades, astronomy may be able to push our observationally based understanding of the universe all the way back to the very first stars.

And thanks to creative thinking, hard work, and excellent use of resources, Stark and his collaborators are giving us a glimpse of what we might learn about early universe today (T+13.7 billion years and counting…)

To learn more about the Keck Telescopes, check out the Keck podcast.

People on Earth have been trying to launch things to Mars since 1960. Of the 44 missions listed in wikipedia (yes, I can be just that lazy), only 17 have been complete successes. This failure to land (or orbitally insert) has caused more than a few editorial cartoons and even some random NASA humor as things ranging from a Mars curse to a Galactic Ghoul to aliens of every imagining have been blamed (mostly with tongue in check). The Mars rovers, Spirit and Opportunity, had seemly put the curse thoroughly in NASA’s past. Launched in 2003, these twin 6 wheeled explorers landed on what was expected to be a 90 day mission way back in January of 2004. Now, roughly 1100 days after bounce down, the rovers are still working, but they are seriously struggling for the first time.

The rovers are powered by solar panels. The initial 90 day life expectancy was based in part on how long NASA engineers believed it would take for dust to accumulate on the panels and cause the computers to shut down. What hadn’t been correctly accounted for was the wind. While dust on the solar panels has caused the rovers to have periodic decreases in power, the wind has consistently blown the dust off the panels, bringing the rovers back up to satisfactory power levels. This year’s storm, however, is not only directly effecting the storms, but it is also so thick that it is blocking 99% of the Sun’s light. If the batteries on the rovers drain entirely, the rovers will not be able to turn back on. Still, its been a good ride and the scientists and engineers who have spent the past couple years monitoring what was supposed to be a three-month mission are to be commended for their dedication (and their spouses deserve a special science-spouse medal!)

But, as one pair of rovers may be facing the end of their mission, another mars explorer is preparing to launch. The Phoenix lander is getting set to launch at the beginning of August. The next launch window for Mars missions opens August 3 and 5:35am EDT. These specific launch windows are set by when the orbits of Mars and Earth are aligned. It takes 2.135 years for the Mars, Earth and Sun to return to the same configuration. In other years, when Mars and Earth are aligned with one another, but not at the same position relative to the Sun, their orbits and their inclinations aren’t optimally aligned for missions to make it from Earth to Mars with minimal fuel. The extreme costs of the journey cause NASA, ESA and other agencies to generally wait for the optimal years.

The Phoenix lander should launch in August, and hopefully land in May of 2008. Unlike NASA’s last three landers that used airbags to safely land, Phoenix will use a parachute to slow and make it’s final approach to the Martian surface using thrusters to slow its descent. Set to land on polar ice, this lander will set itself up to dig and run careful tests on the soil and ice that it finds within reach of its almost 8 ft long arm. This arm will be used to dig through the surface to find and sample stuff below.

Like the Mars rovers, Phoenix is also powered by solar arrays. This mission will last one Martian summer. Just like the Earth’s arctic and antarctic region, during its winter the Martian pole experiences no Sun-light. Thus, with the coming of Martian winter, Phoenix will die. Unlike the mythical animal, it will not be able to resurrect itself, but rather it shall become a part of the Martian ice caps: An artifact of 21st century terrestrial life that will be preserved potentially for eons in the ice of another world.

And, as I stand in awe of the science of WMAP, I also see all the other vast science results that can come out of the CMB. The majority of the results come from simply looking for holes in the constant light of the CMB. For instance, the Sunyaev Zel’dovich effect allows astronomers to find galaxy clusters. As light from the CMB passes through clusters of galaxies, some of the photons interact with high energy electrons - electrons associated with hot gas or accelerated out of some high energy system like a jet. In the interaction, some of the electron and microwave photon exchange energy, and this causes the photon to have a new color (and quite likely a new direction!).

In general, the probability of CMB photons and electrons interacting in any given part of space is very very low (Most of space is empty and lacks electrons the photons can interact with). The only places where there are enough electrons to cause a noticeable number of CMB photons interactions are gas rich, high mass galaxy clusters. By looking for places in the CMB where the distribution of photon colors is a little different, a little higher in energy, astronomers could find galaxy clusters. In reality, astronomers more often look for the Sunyaev Zel’dovich effect where they already see galaxy clusters, and use it to measure the clusters’ densities. It is possible to combine the CMB observations with X-Ray observations, which get at the density of the cluster in a different way, to actually measure the mass and size of distant clusters. One measurement alone isn’t enough, but by studying both X-Ray photons produced by the cluster and the lack of CMB photons (where the “lack of” is also created by the cluster) mass and size can be determined.

Holes and other hills and valleys (more precisely called anisotropies) in the CMB may hide a lot of information. The Oort cloud, which parents long period comets, may also shadow its share of CMB photons. As this cosmic light passes through the cloud of ices and dust, and occasional bona-fide snow balls, some of it scatters. If the Oort cloud is a uniform sphere of snow-like stuff, we may never notice this missing light, but if our solar systems most virgin powder perhaps a bit askew - gravitationally piled up in one place more than another - then will see the 1 part in a lot deviations when we develop better technologies. And with these better technologies, we may also find star formation and dust from AGN.

Every time I read through the titles and abstracts of a new round of papers it seems that something new has been discovered in the light or blocking the light of the CMB. Without this constant light source, science would be far less interesting.

Pick up pretty much any astronomy text, look up Cosmic Microwave Background, and you’ll find something along the lines of: “The Cosmic Microwave Background is a relic of the moment the universe cooled enough for recombination to take place. Prior to that moment the universe was opaque to radiation. Today we see this left over radiation as a 2.725 K degree microwave background radiation.” The book will then go onto explain how the CMB was detected.

Did any of that make sense to you? I know it didn’t make sense to me the first dozen or so times I read it over the years. Let me see if I can make sense of this scientific obstruction for you.

After the Big Bang the universe was hot. Really hot. Dante didn’t have enough levels in hell kind of hot. So hot everything was pure energy. Over time, the universe expanded, and just like the gas expanding as it comes out of a can of compressed air, the expanding universe cooled. By the end of the First Three Minutes (Link goes to book on this by Steven Weinberg) atomic nuclei had solidified, and the universe was a mix of electrons, light, and nuclei. These three things formed a plasma; the same type of stuff that fills fluorescent bulbs and neon lights. In a fully ionized plasma, atoms have no electrons at all. The electrons have such a high energy that they can’t bond to the nuclei! As the electrons and protons interact with one another, they exchange energy, and sometimes they give off photons in the process. They also interact with already existing photons, absorbing them and re-emitting them in new directions and at new colors. In the extremely dense, high-energy plasma of the early universe, the photons were being constantly emitted and re-absorbed, and an individual photon couldn’t travel any appreciable distance (even on the atomic scale!) without being absorbed. It’s this “Can’t get anywhere without being absorbed” part that makes the universe opaque.

Opaque can be taken a couple different ways. My bathroom mirror is opaque because photons can’t go through it (they just bounce off at visible wavelengths). A neon “Open” sign is also opaque, but in this cause it’s because a photon can’t get through it without interacting with the gas and being absorbed (and potentially re-emitted).

So, from about minute 3 to year 380,000 the photons, electrons, and nuclei formed an interacting soup. Then one day, at one specific moment, the universe cooled enough that the electrons and and nuclei could bond. Heat is just a form of energy, and as the universe cooled, the individual electrons lost energy and could eventually bond with atomic nuclei.

For reasons that have never made sense to me, the moment the electrons bonded with the nuclei is called recombination. This was, in fact, the first time the electrons formed lasting bonds with nuclei, so it was the moment of initial combination. Someday I hope to find someone who can explain the name to me who was around when they gave recombination the name recombination. Until then, I’m just going to nod and smile.

As the electrons bonded with the nuclei, they had a bunch of different energies. Some of the electrons were bouncing around fairly slowly, and when they went from free ranging to bound, they gave off a low energy photon. Others were zippying along fairly fast with a high energy, and when they bonded with a nuclei, they gave off high energy photons. Most of the electrons were somewhere in between. If one were to make a plot of the number of photons as a function of color (and this has been done by way more than one astronomer), that plotting person would get a shape called a black body curve. Hot objects, in idealized situations, give off light in a distribution that always has the same shape, but changes in color with temperature. (Check out this neat website for an applet you can play with.)

So, at the moment of combination, which we call recombination, photons flew away from the newly formed atoms with a blackbody distribution of colors. Every single bit of space emitted photons in every direction. This means that no matter where in the universe you are, you will see CMB photons. It also means, as time goes on, we’re going to continue to see CMB photons, but they’ll be photons that formed farther away from us than the ones we’re seeing today. It is as though we are seeing the universe clear out a sphere of stuff for us to look at. Five billion years ago, the CMB originated from a significantly closer point. Had we been able to watch the universe for the past 5 billion years, we might have seen the CMB move away from a spot where the first stars blink appeared to on. Then, we might have seen new galaxies form in that same piece of space that was the furthest visible piece of space when our Sun formed.

It is sad that on human time scales we can’t actually perceive our visible horizon moving away from us.

We will never be able to see beyond the CMB. It is a wall of light that blocks everything that happened before it was formed. The wall is always moving away, but it will always be there.

But that’s okay. It actually does a lot of good, and helps us understand a lot of different things about our universe. I’m going to go into to all the cosmology that we get from the CMB tomorrow, but before I post this post, I’m going to go into one more thing: How the CMB helps us see where we are going.

If you don’t know what doppler shifting is, go read this and play with this.

So, here we are on the planet Earth. As we look at the CMB, we can see in our observations Doppler shifts that come from our motion around the Sun. We can also see our motion around the Milky Way. We can also see our galaxy’s motion in the local group. And, we can also see our local group’s motion as it gets pulled (and not pulled) by the gravity of stuff (and lack of stuff) around us. (A story on voids not pulling can be found in this post).

So, it is because of the Doppler shifts observed in the light of the CMB that we are able to see exactly how we are moving relative to the Universe as a whole. The CMB is uniformly coming from a bit farther away every moment, but its color and brightness doesn’t change in any perceptible way (and given the overall size of the universe, it’s moment-to-moment change in distance doesn’t matter either). This makes the CMB a constant light of constant color that we can use to get amazingly precise Doppler measurements of our own velocity. (image credit: DMR, COBE, NASA. See this link for good explaination)

In essence, the CMB is acting like the beam in a police officer’s radar gun, and all we have to do is build the detector to to catch the beam.

So, while it is really hard (and in practicality impossible) to know exactly where we are in the greater, not fully visible to us, universe, the CMB at least let’s us very accurately measure what direction we are traveling it. And that lets us know where to look to find what is gravitationally pulling (or failing to pull) on our little system as it travels through the vastness of the cosmos.

Two of the most well defined ways we have of studying the universe’s shadows are the Cosmic Microwave Background (CMB) and gravitational lenses. Both things are scientifically interesting in their own right, and each can be used to indirectly see otherwise invisible content in the universe. Recent papers have shown how the CMB may allow astronomers to study our own solar system’s Oort Cloud (the source of long period comets), and how gravitational lensing effects can be used to map dark matter. Rather than try and discuss both these topics in one post, I’m going to take on gravitational lenses today, and dig into the cosmic microwave background tomorrow. (image credit: Kneib & Ellis w/ Caltech Digital Media Center)

The concept of gravitational lensing is perhaps one of the most important in astronomy. Put very simply, just as the gravitational pull of a planet on a comet can cause the comet’s orbit to significantly change shape, so too can the gravity of an object cause the path of light to change. How much the light’s path changes is directly related to the mass of the object the light is passing near. If I shine a flash light past you, the beam will not deviate in a way any measuring apparatus can measure. If I shine a flash light past the Sun, the beam will bend a couple of seconds of arc (It will appear to move about two hair’s width on the sky). If I shine that same light past a black hole (making sure the beam doesn’t enter the event horizon!) the beam might get bent well over 90 degrees! (for mathematical discussion see this neat discussion)

Bending light isn’t a new concept. Lenses and mirrors can both be used to bend light to create magnified, shrunken, and/or distorted images. If I look at an image of myself in a circus mirror, I might appear as an arc of a human; stretched out and distorted in a long curve. This is because the photons that bounce off of me are having their paths distorted by the mirror. In a similar way, a large object (like a galaxy cluster) between us and a distant object (such as a single galaxy), can bend the paths of photons from that distant object and make it appear distorted.

Here is where the neat science comes into play. Dark matter is by definition stuff that exerts gravitational pull on other stuff but can’t otherwise be detected. This means that if we look for objects that are distorted and we can’t find what is doing the distorting, then we can probably blame dark matter. That sounds nice and straightforward, but because the term “distorted” is hard to define in a universe of seemingly (but not actually) infinite possibilities, it is hard to know what is distorted and what is just plan weird looking by nature. Here is where we have to start dealing in generalities. If you take the images of 100 or so galaxies and (after scaling them to have the same radius) average them together, you should get a disk. Some galaxies will be oblong smears pointed from 5 o-clock to 11 o-clock. Others will be boxy cigar shapes aligned from 8 o-clock to 2 o-clock. Others will be plan old circular face-on disks. Averaging all these differences together in a distortion free world gives you a circle every time. Now, if instead of a disk, you find yourself, after averaging, looking at a tear drop shape, or a crescent moon, or any other non-circular shape, then there is something distorting your view on the universe. If you don’t see what is causing the distortions, then what you don’t see is dark matter.

In the past year, there has been a new and exciting stream of results that have used this technique to map the distribution of otherwise hidden materials. The COSMOS survey imaged galaxies, figured out how far away they are, and then measured their average shapes as a function of their distances. This allowed them to say, these nearby galaxies have this type of distortion caused by even more nearby dark matter, while these more distant galaxies have that distortion plus a second distortion that came from dark matter at some intervening distance (think of it as looking through a whole series of distorting pieces of glass with objects randomly placed here and there between different pieces of glass - the distortions add up the more pieces of glass you look through). Their first ever three dimensional map of dark matter did two things: It showed that matter we can see (luminous matter) and dark matter are generally found in the same places but not always, and it showed that dark matter is at least in part, if not in whole, a real physical thing and not just an additional term in the equation for gravity. (credit: NASA / ESA / R. Massey (CalTech))

Other work, observations of both the Bullet cluster and the Zwicky galaxy cluster 0024+1652 were able to map the distribution of dark matter after a collision, and showed that the dark matter can form structures, but doesn’t interact (e.g. collide with stuff) like normal gas or dust. (credit: NASA / ESA / MJ Jee (John Hopkins))

Slowly, using indirect techniques, we are tracing out the features of dark matter. Perhaps Plato would be proud that we have figured out how to find truth in the firelight of the stars and the gravitational shadows dark matter casts on our detectors. Then again, Plato would probably find some existential reason to poo poo our results…

But still, what these people are doing is amazing and beautiful. And gravitational lenses aren’t only used to define dark matter of the “whatever it is, it just isn’t something I understand,” non-baryonic variety, they are also being used to find stuff that is simply too faint or distant to be identified.
Consider mirrors again. If a large mirror (one much bigger than I am) is used to focus light that is reflecting off of me, the image of me may be brighter than if you just looked at me with your eyes! This is because the mirror is capturing more light than your eyes alone would capture. In a similar way, gravitational lenses can also, in some cases, bend more light toward us then would otherwise come our way. This can do two things: It can make an otherwise invisible very distant object visible by lensing it, or it can illuminate the location of an otherwise invisible nearby object that is doing the lensing.

What was for a while the most distant galaxy to be observed was identified as a red, gravitationally lensed pair of smears in an image of the galaxy cluster Abell 2218. This distant galaxy is located more than 13 billion light years away at a redshift of z=5.58. The uneven distribution of galaxies, dust and gas in Abell 2218, split the light of the distant galaxy into two images that are magnified by a factor of about 30. Today, the MACHO and OGLE teams have each looked for the brief (defined on the order of days) brightenings of background stars that occur when a foreground star/planet/dead star orbits in front. These galaxy orbiting objects are generally too faint to otherwise find, and their planets are definitely beyond our abilities to otherwise detect. In this case, out indirect gravitational detections are helping us take a census of the faint non-findable objects hiding in our galaxy’s halo. These things will probably start to become visible as we build bigger infrared telescopes, but until then we can find and count them using gravitational lensing. So far scores of white dwarfs, brown and red dwarfs, black holes, neutron stars and even planets have been found this way. (credit: NASA / ESA / R. Ellis (CalTech) / J.-P. Kneib (Observaoire Midi-Pyrenees))

Unlike standard mirrors and lenses, we have no way to choose where our gravitational lenses will point. We can’t polish them to create perfect images. They only help us see the smallest fraction of what the universe has to show us - but that fraction us stuff that we otherwise wouldn’t ever notice. The invisible is made visible by looking for what isn’t in our images.

But, being a blogger, I’m going to try and get you as far as I can in one posting.

An excellent starting point is, as always, the Cosmic Microwave Background (CMB). This diffuse microwave signal comes from everywhere and lies behind everything. It was formed at the moment the Universe cooled just enough for electrons to combine with atomic nuclei. Prior to that moment, photons couldn’t travel very far without being absorbed by something and then re-emitted with a new color and/or new direction. After that moment, those photons were set free to travel to us today. That moment was called recombination and it occurred roughly 380,000 years after the Big Bang.

Today, 13.7 +/- 0.2 billion years after the Big Bang, we are seeing CMB photons that originated in a sphere of space around the point that would eventually become the place of the Earth. Similarly, photons that originated at the point where the Earth is now located are possibly being observed by aliens at the location where the photons we are seeing originated. Thus, the CMB photons we see are nothing more than a sphere shaped sample of all the photons released during recombination; they are just one small section of the universe. Think of it this way: Imagine the universe as a giant liquid (it is so big we can’t see its edges to define its shape). A scuba diver hovering within the liquid might be able to illuminate the fluid within 10 feet of his head. The fluid beyond the illuminated sphere is still there. It just can never be seen.

Luckily, the universe isn’t a boring liquid, and the light we see isn’t reflecting off any farthest boring visible point. Unfortunately, the photons we see do come from the farthest visible surface of the universe. Luckily, because the universe was a plasma (which behaves loosely like a fluid), any waves propagating through the early universe will be visible to us. Unfortunately, the waves in the early universe have been stretched out to appearing all but flat with the expansion of the universe. Luckily, we have the technology to discern the 1 part in 10,000 remains of the waves.

And what is magical is this: we can use those waves to determine the shape of the universe. If you stand in a room and sing, you will hear your voice come back to you in different ways depending on the shape of the room. At a certain level, it is possible for good forensic scientists to listen to a recording and determine the shape of the room the recording was made within. At a certain level, it is also possible for good cosmologists to determine the shape of the universe based on the waves within the CMB. What we have learned is this: the geometry of the universe is Euclidean. This means parallel lines stay the same distance apart forever. We also know the universe is likely finite. That means that if a line starts at one point and keeps going for a very very very(!!!) long time, it will eventually get back to where it started, just like a line on the surface of a sphere or a torus.

In fact, a torus is a closed Euclidean shape. Two parallel lines on the surface will always stay the same distance apart and they will eventually circle back to their starting point. It is currently thought that our universe is best visualized as a 4 dimensional hyper-torus.
Here I have to admit, I get the geometry but I can’t actually visualize anything expanding from a singularity - a single point - into a donut.

But this I do understand - I am at the center of the universe. And so are you. And so is everything anyone will ever see with a telescope. At one moment - the first moment - the entire universe was a single point, and that point expanded into everything. Imagine a balloon that when empty is a single point. As you blow it up, the balloon expands. Where on the surface of the balloon is the center of balloon? Everywhere. We are on the surface of a multidimensional universe and every point was at the center. Every point. Even my point and your point.
But there are more issues I have to admit to struggling to comprehend. In the shadowlands at the edge of understanding theorists are looking for evidence of pockets of inflation that went at different rates, or perhaps that simply never stopped expanding. They are looking for evidence of Branes, and probing for variations in gravity.

The CMB is mankind’s first and last best hope for understanding our place in the universe.

One of my silly little disappointments with Star Stryder is that no one has asked me what sidereal day means. This could just reflect how skilled everyone has gotten at googling answers, or perhaps Wikipedia has made us all just a bit wiser with its big collective brain. Whatever the reason, I feel like a little kid running around saying, “I learned all about platypuses today,” only to be asked, “What did you learn about the Louisiana Purchase?”

You know, I don’t want to talk about the Louisiana Purchase. I want to talk about platypuses.

Well, actually, I’d like to talk about sidereal days.

If you are given to watching the sunset and wishing on the first star (which may be a planet) you see each night, you may notice that as the constellations wink into visibility they are in a slightly different place each evening twilight. This change occurs for two reasons: sunset occurs at a different time each night, and the alignment between the Sun, Earth and stars is also a little different each night.

I’m going to wait to discuss this first, sunset-time changing problem, until next week, and just take on this change of alignment, sidereal day causing, problem for now.

Let’s start by imagining December 12. On this cold (northern) winter’s day, a person watching the horizon’s of sunrise and sunset would notice the eastern edge of the constellation Ophiuchus just rising in the east at sunrise and the western edge of Ophiuchus just setting in the west at sunset. This means that on December 12, the Sun is planted between us and the often ignored constellation of the Serpent Bearer. If you’re not particularly fond of snakes, this probably sounds like a good place for the Sun to be.

Now consider what the sky will look like 6 months later on a languid day in June - say on June 12 - and look again through our horizon watcher’s eyes. On this probably hot and hazy day, the bull Taurus will appear to poke above the horizon at sunrise and will follow the Sun below the horizon in the evening. Thus, in June, the Sun is placing itself between us and the Bull.

What is actually changing between these two circumstances is how the Earth, Sun and stars are aligned. Let’s extend our constellations as living breathing heros and monsters analogy a bit, and imagine the 12 commonly known zodiacal signs + Ophiuchus arrayed menacingly around the edge of a giant stadium. Now imagine we are huddled together in the center with a very fat yellow rodeo clown. While most rodeo clowns are quick and nimble, this particular clown is actually just a big plastic blowup clown who is nailed to the center of our arena. As we stand, arms length away from our plastic clown, in one location we can see Ophiuchus leering at us over the clown’s shoulders. If we turn our back on the Clown we now find ourself face to face with the red-eye’d Taurus. If we move 180 degrees around the clown, in a mad clockwise dash, we’ll find ourselves peering over the clown’s shoulder at Taurus, but now our back is left exposed to Ophiuchus, and when we put our back to the clown we are face to face with a hero and his snake.

Just as the monster and hero the clown blocked from us varied with our position, the constellation the Sun appears within depends on where our planet is located within its orbit. Each day we move one giant, frantic step clockwise, as the Sun appears to step from Sagittarius to Capricorn to Aquarius as the months move from January to February to March.

So now you know the story of how the Sun moves through the stars. But I haven’t exactly touched on “sidereal day.”

In our day-to-day life we measure our moments relative to the Sun. From midnight-to-midnight we measure one day in a way that is equal to the 24 hour average length between sun-high noon and sun-high noon. But, those of us who study the stars are in need of a different measure of time, one that instead measures the span of time from star-high moment to star-high moment.

The 24 hour day gives us just enough time for the Earth to start out with your nose facing the Sun, and to get rotated through more then 360 degrees as the Earth steps clockwise around the Sun and rotates back to placing you nose-to-Sun once again.

With the stars, not so much rotation is required. They stay in place, and a 360 degree rotation is all that is ever needed.

Consider the star Caph in Cassiopeia. This bright star marks the end of the short arm of the W that is named after a queen. This star lies right off the zero hour line that marks the beginning of time on the sky. If I measure the minutes from Caph passing through the top of the sky - crossing the meridian - to its return to that same high-sky position, I’ll count 23 hours 56 minutes and 4.1 seconds. This span of time is called one sidereal day. The slight differences between a solar measured day and a sidereal day comes from the extra distance the Earth must rotate to point itself back at the Sun from its new position.

Looking at my sidereal time keeping clock, I know that 9 minutes into a new day, Caph passes through its highest position in the sky. I know that Betelgeuse will always pass through its personal high point at 5:55 into the day. Every sidereal day, the stars will always find themselves arrayed in the same way and the same sidereal moment.

It is only the Sun that forces our view to change. So one solar day at a time I live my life, in our Sun driven society, while the stars make their way one sidereal day at a time through our skies.

So, for anyone who cares to ask, when I say I’m blogging one sidereal day at a time, it means my Star Stryder sidereal-daily blog will average 366.24 posts a year instead of the solar days average 365.24 posts per year.