Posted on

Massive clash of black holes raises astronomers’ hopes of witnessing gravitational waves

Artist’s conception of converging supermassive black holes in the Virgo constellation (credit: P. Marenfeld/NOAO/AURA/NSF)

Circling like prizefighters in a ring, a pair of supermassive black holes is heading toward an epic collision. One so powerful it would send a burst of gravitational waves surging through and distorting the very fabric of space-time.

Already, the intensity of the encounter is causing mysterious rhythmic flashes of light coming from quasar PG 1302-102 — 3.5 billion light-years away in the Virgo constellation.

“This is the closest we’ve come to observing two black holes on their way to a massive collision,” said Columbia University astronomer Zoltan Haiman in a new study in the journal Nature.

“Watching this process reach its culmination [confirming the existence of a binary black hole in the relativistic regime by measuring optical and UV brightness] can tell us whether black holes and galaxies grow at the same rate, and ultimately test* a fundamental property of space-time: its ability to carry vibrations called gravitational waves, produced in the last, most violent, stage of the merger.”

The ultimate crash

They estimated the combined and relative mass of PG 1302-102’s black holes, allowing them to narrow down the pair’s predicted crash time: about 100,000 years.

Meanwhile, a recent uptick in the number of black hole binary discoveries has made astronomers hopeful they may in fact witness an actual collision in the next decade and therefore detect gravitational waves, said study coauthor David Schiminovich, also an astronomer at Columbia.

Such a detection would let them “probe the secrets of gravity and test Einstein’s theory in the most extreme environment in our universe — black holes,” said the study’s lead author, Daniel D’Orazio, a graduate student at Columbia. “Getting there is a holy grail of our field.”

* The hope of doing such a test has energized astronomers. Previously, a team led by Matthew Graham, a computational astronomer at the California Institute of Technology, designed an algorithm to pick out repeating light signals from 247,000 quasars monitored by telescopes in Arizona and Australia. Of the 20 pairs of black hole candidates discovered, they focused on the bright quasar. In a January study in Nature, they showed that PG 1302-102 appeared to brighten by 14 percent every five years, indicating the pair was less than a tenth of a light-year apart.

Intrigued, Haiman and his colleagues wondered if they could build a theoretical model to explain the repeating signal. If the black holes were as close as predicted, one had to be circling a much larger counterpart at nearly a tenth of the speed of light, they hypothesized. At that speed, the smaller black hole would appear to brighten as it approached Earth’s line of sight under the relativistic Doppler beaming effect.

If correct, they predicted they would find a five-year cycle in the quasar’s ultraviolet emissions. Analyzing UV observations collected by NASA’s Hubble and GALEX space telescopes they found exactly that.

Abstract of Relativistic boost as the cause of periodicity in a massive black-hole binary candidate

Because most large galaxies contain a central black hole, and galaxies often merge, black-hole binaries are expected to be common in galactic nuclei. Although they cannot be imaged, periodicities in the light curves of quasars have been interpreted as evidence for binaries, most recently in PG 1302-102, which has a short rest-frame optical period of four years. If the orbital period of the black-hole binary matches this value, then for the range of estimated black-hole masses, the components would be separated by 0.007–0.017 parsecs, implying relativistic orbital speeds. There has been much debate over whether black-hole orbits could be smaller than one parsec. Here we report that the amplitude and the sinusoid-like shape of the variability of the light curve of PG 1302-102 can be fitted by relativistic Doppler boosting of emission from a compact, steadily accreting, unequal-mass binary. We predict that brightness variations in the ultraviolet light curve track those in the optical, but with a two to three times larger amplitude. This prediction is relatively insensitive to the details of the emission process, and is consistent with archival ultraviolet data. Follow-up ultraviolet and optical observations in the next few years can further test this prediction and confirm the existence of a binary black hole in the relativistic regime.

Posted on

3D-printed silicone guide with chemical cues helps regenerate complex nerves after injury

3-D scans of a nerve from different angles are used to create a custom regeneration guide for complex nerves (credit: University of Minnesota)

A national team of researchers used a combination of 3-D imaging and 3-D printing techniques to create a custom silicone guide implanted with biochemical cues to help nerve regeneration after an injury.

Nerve regeneration is a complex process, which is why regrowth of nerves after injury or disease is very rare and often permanent, according to the Mayo Clinic.

As a test, the researchers used a 3-D scanner to reverse-engineer the structure of a rat’s sciatic nerve. They then used a specialized, custom-built 3-D printer to print a regeneration guide containing 3D-printed chemical cues to promote both motor and sensory nerve regeneration within the same structure. The guide was then implanted into the rat by surgically grafting it to the cut ends of the nerve. Within about 10 to 12 weeks, the rat’s ability to walk again was improved.

A 3D-printed complex nerve-regeneration pathway implanted in a rat helped to improve walking in 10 to 12 weeks after implantation (credit: University of Minnesota)

“Someday we hope that we could have a 3D scanner and printer right at the hospital to create custom nerve guides right on site to restore nerve function,” said University of Minnesota mechanical engineering professor Michael McAlpine, the study’s lead researcher.

Conventional nerve guidance channels are typically fabricated around cylindrical substrates, so the resulting guidance devices are limited to linear structures. This is is the first time a study has shown the creation of a custom guide for regrowth of a complex nerve like the Y-shaped sciatic nerve, which has both sensory and motor branches.

“The exciting next step would be to implant these guides in humans rather than rats,” McAlpine said. For cases where a patient’s nerve is unavailable for scanning, McAlpine said there could someday be a “library” of scanned nerves from other people or cadavers that hospitals could use to create closely matched 3D-printed guides for patients.

The study by researchers from the University of Minnesota, Virginia Tech, University of Maryland, Princeton University, and Johns Hopkins University was published Thursday (Sept. 17) in the journal Advanced Functional Materials.


UMN College of Science and Engineering | 3D printing of a nerve regeneration guide [no audio]

Abstract of 3D Printed Anatomical Nerve Regeneration Pathways

A 3D printing methodology for the design, optimization, and fabrication of a custom nerve repair technology for the regeneration of complex peripheral nerve injuries containing bifurcating sensory and motor nerve pathways is introduced. The custom scaffolds are deterministically fabricated via a microextrusion printing principle using 3D models, which are reverse engineered from patient anatomies by 3D scanning. The bifurcating pathways are augmented with 3D printed biomimetic physical cues (microgrooves) and path-specific biochemical cues (spatially controlled multicomponent gradients). In vitro studies reveal that 3D printed physical and biochemical cues provide axonal guidance and chemotractant/chemokinetic functionality. In vivo studies examining the regeneration of bifurcated injuries across a 10 mm complex nerve gap in rats showed that the 3D printed scaffolds achieved successful regeneration of complex nerve injuries, resulting in enhanced functional return of the regenerated nerve. This approach suggests the potential of 3D printing toward advancing tissue regeneration in terms of: (1) the customization of scaffold geometries to match inherent tissue anatomies; (2) the integration of biomanufacturing approaches with computational modeling for design, analysis, and optimization; and (3) the enhancement of device properties with spatially controlled physical and biochemical functionalities, all enabled by the same 3D printing process.