Within most galaxies there lurks a supermassive black hole. Our own galaxy, for example contains a black hole 4 million times more massive than our Sun. One of the big mysteries of these black holes is just how they formed, and how long it took for them to reach such a massive size. Now a massive black hole at the edge of the observable universe challenges our understanding of them. 

We discovered this distant black hole because it is a quasar. When a black hole captures nearby material, the material becomes superheated and radiates powerful radio energy and x-rays. These beacons of light are so bright they can only be powered by supermassive black holes. By observing the brightness of distant quasar we can calculate the mass of its black hole engine.

Recently astronomers discovered the most distant quasar ever. Known as J1342+0928, it is so distant we see it from a time when the universe was only 690 million years old. At that time galaxies were just starting to form. But this quasar gives off so much light that its black hole must be 800 million times the mass of our Sun. So how did this particular black hole get so massive so soon? It’s possible that it exists in a rather dense region of space. Having lots of matter around would make it easier to grow quickly. But that isn’t enough to solve the mystery, because the faster a black hole consumes matter, the more light the matter would emit, and that pressure of light and heat would tend to push matter away from the black hole. It’s known as the Eddington limit, and it puts an upper bound on how fast a black hole can grow. To reach 800 million solar masses in such a short time, the black hole would have to consume matter fairly close to this limit.

The big question about this black hole is whether it is simply an unusually early bloomer, or if it is rather typical of black holes in the early universe. To answer that question we will need to find more examples of large quasars on the edge of the cosmos. So the race is on to find these most distant of beacons. If we can find them, they will help us understand how supermassive black holes and their galaxies formed.

The post The Black Hole At The Edge Of The Universe appeared first on One Universe at a Time.

In August I wrote about evidence of a binary supermassive black hole in the center of a galaxy. Now there’s news of another binary in a different galaxy.

The galaxy in question is PG 1302-102, and the light we see has traveled for about 3.5 billion years. Like the other supermassive binary, this galaxy is also a quasar, so it emits a great deal of light from its central region. The team noticed that this particular quasar varied in brightness rather significantly with a period of about 5 years. This could be the sign of two black holes orbiting each other, but it was hard to be sure. So the team created a computer model of a binary system that could explain the variation. What they found is that smaller black hole should be the one causing the most variation in brightness. As the smaller black hole sweeps around the larger one, it captures more material, causing it to superheat.

Given a period of only 5 years, the smaller black hole would need to be moving at nearly 7% of the speed of light. That’s fast enough that special relativity plays a role. If their model was correct, then there should be an even larger variation in brightness at ultraviolet wavelengths. So the team looked at archive data from GALEX and Hubble, which had observed the quasar in the ultraviolet. What they found matched their predictions. All indications are that PG 1302-102 is a supermassive binary.

What’s particularly interesting about this binary is that the two black holes are quite close, about 2,000 astronomical units apart. That’s really close given that their combined mass is on the order of a billion Suns. Within another few hundred thousand orbits, the two black holes will merge with a brilliance of 100 million supernovae.

Paper: Daniel J. D’Orazio, et al. Relativistic boost as the cause of periodicity in a massive black-hole binary candidate. Nature 525, 351–353 (2015)

The post Two Black Holes in a Gravitational Dance appeared first on One Universe at a Time.

A supermassive black hole lurks in the center of our galaxy. But two supermassive black holes lurk in some galaxies.

Since most galaxies contain a black hole in their center, and galaxies have been known to collide, it’s thought that supermassive binary black holes could be relatively common in the universe. We know of some that exist, but they are difficult to confirm. But new research in the Astrophysical Journal has found a supermassive binary in the heart of a quasar.

Quasars are extremely bright sources of energy, powered by the superheated material (the accretion disk) near a black hole. They are so luminous that it’s impossible to resolve a supermassive binary directly. But a close binary black hole would clear out the region between the black holes, leaving a gap in the surrounding material. This gap would lower the overall temperature of the accretion disk, and that means less ultraviolet light should be emitted by the quasar. In this work, the team compared the visible and ultraviolet spectrum of a quasar known as Markarian 231. They found a weaker ultraviolet spectrum, just as expected for a supermassive binary.

What’s great about this research is that it allows us to find supermassive binary black holes by looking at the spectra of quasars. So it’s quite likely that the method could be used to find many more of these twin giants.

Paper: Chang-Shuo Yan et al. A Probable Milli-parsec Supermassive Binary Black Hole in the Nearest Quasar Mrk 231. ApJ 809 117 (2015)

The post Twin Giants appeared first on One Universe at a Time.

Quasars are very bright objects that are generally billions of light years away. We now know that they are a kind of active galactic nuclei (AGN) and are powered by supermassive black holes in the centers of galaxies. We know this in part because they emanate from within galaxies, and their energy comes from a region only a few light years across. But how do we know the size of something from billions of light years away?

At that distance, a quasar is too small for us to measure its size directly, but we can do it indirectly by measuring the variation in a quasar’s brightness. Take, for example, the brightest quasar in our sky (in the visible spectrum) known as 3C 273. It’s redshift puts it at about 2.5 billion light years away. Because of its brightness and relative closeness, it is one of the most studied quasars. So we actually have quite a bit of data on it. One of the things we’ve observed is that its brightness oscillates over time, getting slightly brighter and dimmer about 15 times a year. We see this variability in other quasars, but 3C 273 is the most accurately measured.

Quasars plotted as a function of their size.

A varying brightness is interesting because it tells us something about the size of the source. Basically if an object is changing brightness, it can’t do that at a rate faster than the time it takes one side of the object to know what the other side is doing. That time is limited by the speed of light, so if you know the rate at which brightness varies, you know the maximum possible size of the object. Since these objects are also greatly redshifted we have to account for that as well (high redshift means time dilation), but that’s pretty easy to do. So we can take our quasar and AGN observations and calculate a maximum size for each one. Taking data for various quasars, I’ve plotted how many are at each particular size. While they vary in size, the most common size is most commonly around 5 on this graph, which equates to 100,000 AU, or about 1.5 light years across.

That might seem pretty big, but remember that these objects are brighter than our galaxy (consisting of 200 billion stars). On a galactic scale these objects are tiny. Given their large brightness and tiny size, we can say pretty confidently that they are powered by black holes. There’s other evidence to support this conclusion, but that’s a story for another time.

The post Sizing Things Up appeared first on One Universe at a Time.

Modern cosmology is dominated by two fundamental theories: general relativity, which describes the structure of space and time as manifold that interacts with mass/energy (aka gravity), and quantum theory, which describes the fundamental interactions of protons, electrons, light, etc. (aka quanta). Both models are strongly supported by experimental and observational evidence. The problem is that each theory makes fundamental assumptions about the way the universe works, and they contradict each other at a basic level. This isn’t a problem if you are interested in things on a large scale, such as planets and galaxies (general relativity), or things on a small scale such as nuclear fusion (quantum theory). The contradiction arises when you want to understand objects that are both very dense and interact at high energies, such as black hole interiors, the big bang, etc. So one of the challenges of modern cosmology is to develop a unified theory of quantum gravity, which would combine the predictions of general relativity and quantum theory in a consistent way.

There are lots of approaches to quantum gravity, including string theory and loop quantum gravity, that try to unify these two models, but one of the big challenges is that many of their predictions are difficult if not impossible to verify. But new observations of distant quasars has put some observational constraints on the type of unified model the universe might allow.

The research focuses on a property common to most unified theory approaches, known as quantum foam. The idea behind quantum foam is that at a fundamental level the quantum aspect of things dominates. This means that on a small enough scale, the precise nature of space and time itself breaks down into a nebulous flurry of quantum fluctuations or quantum foam. In this approach the structure of space and time we see around us is a macroscopic approximation arising out of this foam, just as a table appears solid when in fact it is a dynamic interaction of atoms and molecules. The scale at which the foamy nature of spacetime becomes evident is known as the Planck scale, which is about 10 billionths of the width of a proton. That’s far too small for us to probe directly.

But it turns out that this quantum foam (assuming it exists) should interact very slightly with light. Basically, a photon traveling through spacetime has a tiny chance of interacting with the quantum foam in such a way that its wavelength and direction could be changed. The chances of such an interaction is so small as to almost be zero, but over a billion light year journey it would have a measurable effect. Depending on the quantum foam modal, distant light could appear blurred at certain wavelengths so that our view of distant quasars would become too blurry to be observed.

Based upon observations of distant quasars, the team found no evidence of any quantum foam blurring. Given the constraints of their observations, this means that spacetime is completely smooth down to a scale of at least a thousandth of the width of a proton. This is actually precise enough to eliminate some quantum foam models. In particular, it eliminates one popular model known as the holographic model. As the authors point out, while the holographic model is a popular model relying upon the holographic principle, this research doesn’t invalidate the holographic principle itself.

So to the limits of observation, there is no evidence for a quantum foam. Whether it exists but has more subtle effects is something that will require further research.

Paper: E. S. Perlman et al. New Constraints on Quantum Gravity from X-ray and Gamma-Ray Observations. ApJ 805 10 doi:10.1088/0004-637X/805/1/10 (2015)

The post Foamy Evidence appeared first on One Universe at a Time.

Quasars were once known as quasi-stellar radio sources due to their intense but nearly point-like source of radio energy. When first discovered in the 1930s, little was known about their underlying cause. By the 1950s we knew by their redshifts that they were billions of light years away, which meant they must be unbelievably luminous. We now know that quasars are active galactic nuclei, powered by supermassive black holes in the centers of galaxies. Quasars occur when the black hole of a young galaxy consumes large quantities of gas and dust. During this active stage of the black hole the material is superheated and large jets can be emitted by the black hole. It’s thought that most, if not all, galaxies enter such a stage in their youth, but this intense active period is short-lived on a cosmic scale. So it’s unusual to see several quasars clustered together. But now we’ve found a rare quartet of quasars, and it’s raising a few eyebrows.

The discovery was presented in the latest issue of Science, which finds four quasars in a single large nebula. The nebula is about a million light years across and has a mass of about 100 billion Suns, which is surprisingly large. But the presence of four active galactic nuclei is highly unusual. Quasars make up a relatively small fraction of galaxies, so the odds of four of them being so closely packed purely by chance is about 1 in 10 million. This would seem to imply that they have some kind of common origin, but it’s unclear what that might be. The usual computer simulations don’t predict this kind of close quasar alignment.

It’s possible that this is just an odd random clustering, or it’s possible that our models of galaxy formation might have to be tweaked, but it’s too early to tell at this point.

Paper: Hennawi et al. Quasar quartet embedded in giant nebula reveals rare massive structure in distant universe. 348 (6236): 779-783 (2015)

The post Four in a Row appeared first on One Universe at a Time.

The wispy green clouds seen in these galaxies are unusual because they are so bright. They are emission nebula stimulated into glowing due to a burst of ultraviolet light. That by itself isn’t unusual, but the central quasars aren’t particularly bright. The brightness of these surrounding clouds indicates that the quasars were quite bright in the past. 

Given the scale of these clouds and their current brightness, the light stimulating the emission originated from the quasar tens of thousands of years ago. That might seem like a long time for a quasar to go quiet, but on a cosmic scale that’s pretty fast, and quasars don’t typically vary much in brightness. So what’s going on?

One idea is that the quasars are powered not by one supermassive black hole, but two. Two closely orbiting black holes could disrupt the flow of matter into each other, and this would cause the brightness of the quasar to vary. This would seem to be supported by the shape of the clouds themselves, which tend to have a twisted, spiral shape indicative of merged galaxies.

The post Green Goblins appeared first on One Universe at a Time.

Black holes come in a range of sizes, from star-massed ones of a few solar masses to supermassive ones containing millions, sometimes billions of solar masses. Recently, we’ve found one on the larger end of that range, with a mass of about 12 billion Suns. While we’ve found other black holes of similar mass, this one is unusual because of its distance, and it has us scratching our heads a bit over just how it formed.

Credit: Zhaoyu Li/Yunnan Observatories

The black hole has been observed as a quasar with a redshift of about 6.30. This means the light from the quasar has been traveling for about 12.8 billion years. You might think that means it is 12.8 billion light years away, but due to cosmic expansion it’s actually much more distant. With such a high redshift, the light we observe is when the observable universe was only 900 million years old. It’s also the brightest quasar ever discovered. So how did such a massive black hole form so early in the universe? A black hole could achieve its size by capturing matter at nearly the maximum rate for a black hole, but it’s so bright that the radiation it gives off would work to limit the rate at which surrounding matter could be captured. A more likely scenario is that the black hole is a result of a merger between two supermassive black holes.

At this point we aren’t sure of its origin. But having such a bright quasar so far away does have advantages. Since the light of the quasar travels a great distance to reach us, we can use bright quasars like this to study any gas and dust between it and us. This particular quasar will let us study more distant material.

Paper: Xue-Bing Wu, et al. An ultraluminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30. Nature 518, 512–515 (2015)

The post That’s a Big Twinkie appeared first on One Universe at a Time.

Radio astronomy is incredibly precise. This is particularly true when they’re used in combination through a process known as Very Long Baseline Interferometry (VLBI). It is so precise that by observing quasars we can measure not only changes in Earth’s rotation, but also tectonic drift between radio telescopes.

The way VLBI works is by measuring how long it takes for fluctuations in a quasar’s light to reach different radio telescopes. Since light travels at a constant rate, the difference in arrival time can be used to determine the difference in distance. Using an array of telescopes you can determine not only the distance between the telescopes, but the precise location of the signal. VBLI can determine the distance between antennas within millimeters, and the position of a radio source to within a fraction of a milliarcsecond.

Because quasars are so distant, they can be treated as fixed points of reference in space. This makes them useful for determining the motion of objects relative to them, such as the precise motion of Saturn, or the Magellanic clouds. But because they are fixed points in the sky, any shift in the location or timing of quasars must necessarily be due to a change in the position of the telescopes themselves, or the rotation of the Earth.

What’s amazing about this technique is that it uses objects billions of light years away to measure millimeter shifts in position on the Earth.

The post Marking Time appeared first on One Universe at a Time.

There’s been press recently that astronomers have discovered a “spooky” or “mysterious” alignment of quasars across the universe. While such claims make great headlines, the new results aren’t spooky at all, nor are they that mysterious. They are somewhat interesting, so it’s worth discussing.

The headlines are based on a new paper in Astronomy and Astrophysics that looks at the polarization of quasars in large cosmic structures. A quasar is an intense source of energy powered by a supermassive black hole in the center of a galaxy. Often the light from a quasar is polarized, meaning it has a particular orientation. This new paper looked at the polarization of 93 quasars with good data.

It turns out that there are two ways that quasar light can be polarized. The first is due to the diffuse gas and dust between the quasar and us. Lots of light sources are polarized by the interstellar medium, and quasar signals are no exception. The second is that the quasars can be inherently polarized. This second case is useful because inherent polarization is typically either parallel or perpendicular to the rotational axis of the black hole and surrounding galaxy, so knowing the polarization you know something of a galaxy’s rotational alignment.

We can’t always tell the difference between the two types of polarization, but when the polarization is particularly sharp, it’s almost always due to an inherent polarization of the quasar. Of the 93 quasars in this particular study, 19 had sharp polarizations. So the authors looked at these 19 quasars, and found that their inherent polarizations tended to align with the structure of their galaxy clusters. On very large scales, the universe tends to be super large clumps of galaxies connected by diffuse filaments of stars and galaxies. So the quasar polarizations tended to align with the filaments. This would imply that their galaxies are also aligned with the filaments.

The odds of this happening purely by chance is about 1%, which makes it unusual, but not astoundingly so. What’s more interesting is that these filaments can span billions of light years, so the quasar alignments are over the same range. Does that make it spooky? Not really. In fact computer simulations of cosmic evolution actually predict some correlation between filaments and galaxy alignment. This new work is the first observational evidence of such an alignment. The level of observed is somewhat higher than predicted levels, which could suggest a deeper underlying mechanism, but the evidence isn’t strong enough to make that conclusion solid.

So what we’ve found here is not something spooky, it is just evidence of more complexity within the structure of the universe.

Paper: Damien Hutsemékers, et al. Alignment of quasar polarizations with large-scale structures. A&A 572, A18 (2014)

The post Not So Spooky appeared first on One Universe at a Time.

Quasars are among the most energetic things in the universe, and are intense sources of radio waves and visible light. Because of their great distance, they appeared almost point-like to early observers. Thus they were given the name quasi-stellar radio sources, or quasars for short. For several decades the source of their great power was a mystery, but we know know that they are powered by active supermassive black holes in the centers of galaxies. As we’ve observed more quasars, we’ve found that they can vary significantly in brightness, redshift, and line spectra.

But despite this variety, there are some commonalities. One big commonality is known as Eigenvector 1, which traces correlations between emission lines of iron, oxygen and hydrogen, which in turn correlates with properties such as x-ray strength and the like. Eigenvector 1 was first discovered in 1992, so we’ve long known that it works, but why it works has been a bit of a mystery. Now a new paper in Nature may shed light on that mystery.

In this new work, the authors looked at two line spectra properties: the width of an emission line called hydrogen beta (Hβ) and the strength of an iron emission line known as Fe II. These are useful because they are known to correlate with specific properties of quasars.

The broadness of Hβ is a measure of the rotational motion of the accretion disc along our line of sight. As the material of the accretion disk rotates about the black hole, one edge of the disk is moving toward us slightly, while the other edge of the disk is moving away from us slightly. This means light from one edge is slightly blueshifted, while the other edge is slightly redshifted. This is an effect called line broadening. Since the speed of material in a black hole accretion disk is fairly consistent, the broadness of Hβ is a good measure for the orientation of the accretion disk relative to our line of sight. A broad line indicates an almost edge-on view, while a narrow one means the disk is almost face-on.

The Fe II line is connected to Eigenvector 1, and the strength of the Fe II line has been suspected to be a good measure of the efficiency at which the black hole accretes matter. Specifically, it seems to be a good measure for the Eddington ratio, which is the ratio of its rate of accretion to the maximum theoretical limit. So basically, these two lines are a measure of the orientation and energetic efficiency of quasars.

Credit: Shen and Ho

The authors then gathered the line spectra observations of 20,000 quasars and plotted them as a function of Hβ and Fe II. What they found was that the quasars cluster within a wedge. Given this wedge shape, it seems pretty clear that Fe II is, in fact a good measure of the Eddington ratio. The peak strength of Fe II aligns well with the orientation of the accretion disk.

What’s particularly striking about this graph is that it follows a similar method to that of the Hertzsprung-Russell (or HR) diagram. The HR diagram is a plot of stars by their brightness and color. When it was first developed around 1910, it revolutionized our understanding of stellar evolution by demonstrating that stars tend to cluster along a line known as the main sequence. We’ll have to wait and see if this new diagram for quasars leads to a revolution in our understanding of quasars and other active galactic nuclei, but it seems clear that this new work has a great deal of potential.

Paper: Yue Shen & Luis C. Ho. The diversity of quasars unified by accretion and orientation. Nature 513, 210–213. (2014)

The post Orienting Eddington appeared first on One Universe at a Time.

A couple days ago I wrote about a rather large cluster of quasars, and how it seemed to be larger than we’d expect for the universe as we know it. The post gathered the attention of an anonymous commenter, who pointed out an opposing view regarding this research. The rebuttal to the cluster research was published in MNRAS, and makes a rather simple claim: not all patterns are real. In other words, if you look deep enough for a pattern in your data, you are bound to find one, even if it is really just noise. 

The argument that “you can always find a pattern if you look for one” is a pretty standard rebuttal in data analysis. It is much like the old “correlation is not causation” argument. While both statements are basically true, simply stating them doesn’t buy you much. In data analysis, distinguishing the signal from the noise is a central part of the work, so we’re generally pretty careful to avoid false positives. So if you’re going to counter a research finding with “it’s just noise” you better be able to back up your claim with solid evidence. In this case, the new paper makes a pretty solid argument. As the author points out, what constitutes a “structure” depends a great deal how you define your connections between objects.

As an example, suppose you wanted to define the typical size of a person’s community. You could define a person’s community as only those people who are close friends. By that definition most communities would be quite small, usually less than a dozen. That’s probably not very accurate, so you could extend it to close friends and close acquaintances. Or perhaps even more broadly friends, acquaintances and their acquaintances. Define things too broadly and all of humanity is in the single community of Kevin Bacon. Define it too narrowly and we all look like social recluses. The reality is somewhere in the middle, with a mix of friends and acquaintances.

With quasars you can use a similar definition. Specifically, if two quasars are within a certain distance of each other, they can be considered part of the same cluster. If a third quasar is within that distance of either of the other two, it is also part of the cluster, and so on. Obviously, the distance you define for the will affect the scale of your cluster. Make that distance too small, and clusters are small and rare. Make it too large, and you get a cluster that spans most of the universe. In the original paper the minimum distance was set at 100 megaparsecs, or about 325 million light years.  That’s pretty big considering that our local cluster of galaxies (the local group) is only about 10 megaparsecs across. But is that distance too big to be meaningful? This new paper argues that it is.

Left: The “cluster” showing only members of the cluster with large dots. Right: The same region with smaller dots including non-cluster quasars. Credit: Clowes/Nadathur

To demonstrate this, the author looked at just how likely false positives were under this definition. They ran simulations of randomly distributed quasars, so that they satisfied the condition of homogeneity, then calculated how often a super-large cluster appeared by chance alone. The result was that such super clusters were rather common. Finding a cluster 4 billion light years wide isn’t that unusual. So it’s hard to say that the cluster is a legitimate structure. It certainly shouldn’t be seen as very unusual.

On their blog, the author hammers the point home by visually comparing the cluster with other quasars in the region, as you can see in the figure. If you only include members of the cluster and make your dots big, then it seems pretty clear. If you make the dots smaller and include all quasars in the region, the cluster doesn’t look quite as convincing.

Sometimes a mystery raises deep questions about our understanding of the cosmos. Sometimes it simply fades away when you look at things a bit more carefully.

Paper: Seshadri Nadathur. Seeing patterns in noise: gigaparsec-scale ‘structures’ that do not violate homogeneity.  MNRAS 434 (1): 398-406. doi: 10.1093/mnras/stt1028 (2013)

The post Calling the Question appeared first on One Universe at a Time.