New Research Shows that Short Gamma-Ray Bursts are Powered through Formation of Neutron Stars as well as Black Holes

        An artist's impression of a gamma-ray burst powered by a neutron star. Credit: Nuria Jordana-Mitjans

An international collaboration led out of the University of Bath has reported early measurements of a short-duration gamma-ray burst that challenge the standard paradigm for these phenomena. The source, GRB 180618A, was observed with space-and ground-based telescopes to construct a time sequence of emission from gamma-ray through optical wavelengths.

Observations with the Large Binocular Telescope obtained by LBTO and INAF astronomers were used to locate the galaxy where the transient event occurred. Deep-field observations from the Large Binocular Cameras and high-precision spectroscopic data from the Multi-Object Double Spectrographs revealed a galactic trio 10.6 billion light years away. Further examination of the LBT data indicated that the GRB exploded at the outskirts of one of these galaxies.

Analysis of the measured GRB emission points to an origin from a wind nebula powered by a young, highly magnetized neutron star, known as a magnetar. Previous studies of short GRBs implicated the merger of a binary pair of neutron stars that form a black hole as the source of energy driving the explosion. The new results also point to the merger of a neutron star binary as the precipitating event, but with a product that is itself a massive neutron star, accompanied by a release of gravitational and magnetic energy. The conclusion is that at least two types of merger processes underlie short-duration gamma-ray bursts.

The new results are reported in the published article by Jordana-Mitjans et al. (2022), Astrophys. Jour., 939, 106

Red-Supergiant Supernova Images Reveal Secrets of an Earlier Universe

   The above image shows the light from the supernova behind the galaxy cluster Abell 370. Photo credit: Wenlei Chen, NASA

The above image shows the light from the supernova behind the galaxy cluster Abell 370. Photo credit: Wenlei Chen, NASA

A new study has measured the size of a star that exploded more than 11 billion years ago. Detailed images show the exploding star cooling and could help scientists learn more about the stars and galaxies present in the early universe.

The findings are published in Chen et al. (2022), Nature, 611, 256.

“This is the first detailed look at a supernova at a much earlier stage of the universe’s evolution,” said Patrick Kelly, a lead author of the paper and an associate professor in the University of Minnesota College of Science and Engineering. “It's very exciting because we can learn in detail about an individual star when the universe was less than a fifth of its current age, and begin to understand if the stars that existed many billions of years ago are different from the ones nearby.”

The red supergiant in question was about 500 times larger than the sun, and it’s located about 60 times farther away than any other supernova observed in this detail.

Using data from the Hubble Space Telescope and the Large Binocular Telescope, researchers were able to identify multiple detailed images of the red supergiant because of a phenomenon called gravitational lensing, where mass, such as that in a galaxy, bends light. This magnifies the light emitted from the star.

“The gravitational lens acts as a natural magnifying glass and multiplies Hubble’s power by a factor of eight,” Kelly said. “The images we captured show the supernova as it was at different ages separated by several days. We see the supernova rapidly cooling, which allows us to basically reconstruct what happened and study how the supernova cooled in its first few days with just one set of images. It enables us to see a rerun of a supernova.”

The researchers combined this discovery with another one of Kelly’s supernova discoveries from 2014 to estimate how many stars were exploding when the Universe was a small fraction of its current age. They found that there were likely many more supernovae than previously thought.

“Core-collapse supernovae mark the deaths of massive, short-lived stars. The number of core-collapse supernovae we detect can be used to understand how many massive stars were formed in galaxies when the Universe was much younger,” said Wenlei Chen, first author of the paper and a University of Minnesota postdoctoral researcher .

The research was funded by the National Science Foundation; the Hubble Space Telescope Cycle 27 Archival Research and Frontier Fields program; the World Premier International Research Center Initiative, MEXT, Japan; the United States-Israel Binational Science Foundation; the Ministry of Science & Technology, Israel; the Christopher R. Redlich Fund; and the University of California, Berkeley Miller Institute for Basic Research in Science.

Primordial Helium Research at the Large Binocular Telescope

A recent news story from Gonzaga University reports on research by Gonzaga Professor Erik Aver using the Large Binocular Telescope to study the primordial helium abundance. The work, conducted in collaboration with Richard Pogge at Ohio State University and Evan Skillman at the University of Minnesota, was recently awarded major support through a grant of $755k from the National Science Foundation.

The study will make use of LBT spectra of more than 40 metal-poor galaxies analyzed with advanced methods to measure a value for the primordial helium abundance with an uncertainty of approximately 0.5%. The resulting increase in precision will be significant as a constraint on proposed scenarios for extending the standard model of particle physics. 

Dual and Lensed Active Galactic Nuclei at Sub-arcsecond Separations Revealed through HST and LBT Observations

A recent study led by Filippo Mannucci (INAF/Osservatorio Astrofisico di Arcetri) reported observations by the Large Binocular Telescope and Hubble Space Telescope confirming candidates for multiple supermassive black holes at small angular separation.

These objects, identified as active galactic nuclei based on the radiative signature of matter accreting onto the central compact object, were selected as potential multiple systems based on measurements from the Gaia satellite suggesting the presence of more than one peak in the light distribution seen on the sky. The LBT and HST delivered high angular resolution images allowing the sources to be seen as distinct pairs or multiple sources for the first time.

Dual supermassive black holes are of interest as candidates for merging systems that will ultimately spiral together while releasing huge amounts of energy in gravitational waves. Models tracing the formation and development of galaxies, along with their central black holes, predict the occurrence of such mergers as they evolve over cosmic time.

Multiple systems can alternatively represent images of a single active galactic nucleus, produced through the bending of light by a massive object at intermediate distance, through a process known as gravitational lensing. Gravitational lenses provide a novel means for tracing the distribution of dark matter and measuring cosmological parameters.

The LBT measurements made use of the LUCI1 infrared camera assisted by the SOUL implementation of natural guide-star, single conjugate adaptive optics.

The results are published in Mannucci et al. (2022),Nature Astronomy, 6, 1185

LBT Observations Confirm Exoplanet Candidates Identified by Gaia

The Gaia spacecraft, designed to map the three-dimensional structure of our Galaxy, has provided a rich database of precision measurements enabling other types of science, most recently the discovery of exoplanets orbiting target stars. In a recent report by Aviad Panahi (Tel Aviv University) and collaborators, Gaia photometry was used for the first time to identify candidate exoplanet transit events, signaled by a dip in a star’s brightness as an orbiting planet passes along our line of sight and covers a part of the stellar disk.

Confirmation that the temporary dimming was the result of an orbiting exoplanet was obtained for two sources, with spectra from the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) on the Large Binocular Telescope. The data acquired over multiple epochs provide sensitive measures of the star’s radial velocity (i.e. speed of motion along our line of sight) which oscillates over time as the star is pulled by the gravity of an orbiting planet.

The LBT data enable estimation of the planets’ mass which in both cases resembles that of Jupiter. However, the newly discovered exoplanets orbit in close proximity to their parent stars, with periods of only 3 – 4 days, resulting in surface temperatures in excess of 1000 K. The discovery of these “hot jupiters” is an important demonstration of the potential for Gaia to extend the census of extrasolar planets.

The study findings are reported in Panahi et al. 2022, Astronomy & Astrophysics, 663, A101

A weird star produced the fastest nova on record

A team of users of the Large Binocular Telescope has recorded the fastest nova ever. They hope to find answers to not only the nova’s many baffling traits, but to larger questions about our solar system and the universe.

Astronomers are buzzing after observing the fastest nova ever recorded. The unusual event drew scientists’ attention to an even more unusual star. As they study it, they may find answers to not only the nova’s many baffling traits, but to larger questions about the chemistry of our solar system, the death of stars and the evolution of the universe.

The research team, led by Arizona State University Regents Professor Sumner Starrfield, Professor Charles Woodward from University of Minnesota and Research Scientist Mark Wagner from The Ohio State University, co-authored a report published in the Research Notes of the American Astronomical Society.

 A nova is a sudden explosion of bright light from a two-star system. Every nova is created by a white dwarf — the very dense leftover core of a star — and a nearby companion star. Over time, the white dwarf draws matter from its companion, which falls onto the white dwarf. The white dwarf heats this material, causing an uncontrolled reaction that releases a burst of energy. The explosion shoots the matter away at high speeds, which we observe as visible light.

The bright nova usually fades over a couple of weeks or longer. On June 12, 2021, the nova V1674 Hercules burst so bright that it was visible to the naked eye — but in just over one day, it was faint once more. It was like someone flicked a flashlight on and off.

Nova events at this level of speed are rare, making this nova a precious study subject.

“It was only about one day, and the previous fastest nova was one we studied back in 1991, V838 Herculis, which declined in about two or three days,” says Starrfield, an astrophysicist in ASU’s School of Earth and Space Exploration.

As the astronomy world watched V1674 Hercules, other researchers found that its speed wasn’t its only unusual trait. The light and energy it sends out is also pulsing like the sound of a reverberating bell.

Every 501 seconds, there’s a wobble that observers can see in both visible light waves and X-rays. A year after its explosion, the nova is still showing this wobble, and it seems it’s been going on for even longer. Starrfield and his colleagues have continued to study this quirk.

“The most unusual thing is that this oscillation was seen before the outburst, but it was also evident when the nova was some 10 magnitudes brighter,” says Wagner, who is also the head of science at the Large Binocular Telescope Observatory being used to observe the nova. “A mystery that people are trying to wrestle with is what’s driving this periodicity that you would see it over that range of brightness in the system.”

The team also noticed something strange as they monitored the matter ejected by the nova explosion — some kind of wind, which may be dependent on the positions of the white dwarf and its companion star, is shaping the flow of material into space surrounding the system.

This illustration shows an intermediate polar system, a type of two-star system that the research team thinks V1674 Hercules belongs to.  A flow of gas from the large companion star impacts an accretion disk before flowing along magnetic field lines onto the white dwarf.    Credit: Illustration by Mark Garlick. 

Though the fastest nova is (literally) flashy, the reason it’s worth further study is that novae can tell us important information about our solar system and even the universe as a whole.

A white dwarf collects and alters matter, then seasons the surrounding space with new material during a nova explosion. It’s an important part of the cycle of matter in space. The materials ejected by novae will eventually form new stellar systems. Such events helped form our solar system as well, ensuring that Earth is more than a lump of carbon.

 “We're always trying to figure out how the solar system formed, where the chemical elements in the solar system came from,” Starrfield says. “One of the things that we're going to learn from this nova is, for example, how much lithium was produced by this explosion. We're fairly sure now that a significant fraction of the lithium that we have on the Earth was produced by these kinds of explosions.”

Sometimes a white dwarf star doesn’t lose all of its collected matter during a nova explosion, so with each cycle, it gains mass. This would eventually make it unstable, and the white dwarf could generate a type 1a supernova, which is one of the brightest events in the universe. Each type 1a supernova reaches the same level of brightness, so they are known as standard candles.

“Standard candles are so bright that we can see them at great distances across the universe. By looking at how the brightness of light changes, we can ask questions about how the universe is accelerating or about the overall three-dimensional structure of the universe,” Woodward says. “This is one of the interesting reasons that we study some of these systems.”

Additionally, novae can tell us more about how stars in binary systems evolve to their death, a process that is not well understood. They also act as living laboratories where scientists can see nuclear physics in action and test theoretical concepts.

The nova took the astronomy world by surprise. It wasn’t on scientists’ radar until an amateur astronomer from Japan, Seidji Ueda, discovered and reported it.

MODS1 & MODS2, the pair of LBTO multi-object double spectrographs used by the team, seen while the telescope is pointed at horizon. Photo credit: Rick Pogge.

Citizen scientists play an increasingly important role in the field of astronomy, as does modern technology. Even though it is now too faint for other types of telescopes to see, the team is still able to monitor the nova thanks to the Large Binocular Telescope’s wide aperture and its observatory’s other equipment, including its pair of multi-object double spectrographs (MODS) and exceptional PEPSI high resolution spectrograph.

They plan to investigate the cause of the outburst and the processes that led to it, the reason for its record-breaking decline, the forces behind the observed wind, and the cause of its pulsing brightness.

AN UNEXPECTED GAMMA RAY BURST

An international group led by INAF researchers have confirmed that the gamma-ray burst GRB 200826A, which lasted less than two seconds – typical of short bursts – is associated with the explosion of a massive star, which is typical of long gamma-ray bursts. The study, involving also several universities and research institutes in Italy, is primarily based on data collected with the Large Binocular Telescope in Arizona, USA. The observations made the first ever use of adaptive optics to observe a supernova associated with a gamma-ray burst.