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New work from the Carnegie Supernova Project provides the best-yet calibrations for using type Ia supernovae to measure cosmic distances, which has implications for our understanding of how fast the universe is expanding and the role dark energy may play in driving this process. Led by Carnegie astronomer Chris Burns, the team's findings are published in The Astrophysical Journal.

An artist's conception of what's called the cosmic distance ladder -- a series of celestial objects, including type Ia supernovae that have known distances and can be used to calculate the rate at which the universe is expanding [Credit: NASA/JPL-Caltech]

Type Ia supernovae are fantastically bright stellar phenomena. They are violent explosions of a white dwarf--the crystalline remnant of a star that has exhausted its nuclear fuel--which is part of a binary system with another star.

In addition to being exciting to observe in their own right, type Ia supernovae are also a vital tool that astronomers use as a kind of cosmic mile marker to infer the distances of celestial objects.

While the precise details of the explosion are still unknown, it is believed that they are triggered when the white dwarf approaches a critical mass, so the brightness of the phenomenon is predictable from the energy of the explosion. The difference between the predicted brightness and the brightness observed from Earth tells us the distance to the supernova.

Astronomers employ these precise distance measurements, along with the speed at which their host galaxies are receding, to determine the rate at which the universe is expanding. Thanks to the finite speed of light, not only can we measure how quickly the universe is expanding right now, but by looking farther and farther out into space, we see further back in time and can measure how fast the universe was expanding in the distant past. This led to the astonishing discovery in the late-1990s that the universe's expansion is currently speeding up due to the repulsive effect of a mysterious "dark" energy. Improving the distance estimates made using type Ia supernovae will help astronomers better understand the role that dark energy plays in this cosmic expansion.

"Beginning with its namesake, Edwin Hubble, Carnegie astronomers have a long history of working on the Hubble constant, including vital contributions to our understanding of the universe's expansion made by Alan Sandage and Wendy Freedman," said Observatories Director John Mulchaey.

This is an artist's conception shows a type Ia supernova exploding [Credit: ESO]

However, the speed at which the brightness of type Ia supernova explosions fade away is not uniform. In 1993, Carnegie astronomer Mark Phillips showed that the explosions that take longer to fade away are intrinsically brighter than those that fade away quickly. This correlation, which is commonly referred to as the Phillips relation, allowed a group of astronomers in Chile, includingPhillips and Texas A&M astronomer Nicholas Suntzeff, to develop type Ia supernovae into a precise tool for measuring the expansion of the universe.

Studying the supernovae using the near-infrared part of the spectrum was crucial to this finding. The light from these explosions must travel through cosmic dust to reach our telescopes, and these fine-grained interstellar particles obscure light on the blue end of the spectrum more than they do light from the red end of the spectrum in the same manner as smoke from a forest fire makes everything appear redder. This can trick astronomers into thinking that a supernova is farther away than it is. But working in the infrared allows astronomers to peer more clearly through this dusty veil.

"One of the Carnegie Supernova Project's primary goals has been to provide a reliable, high-quality sample of supernovae and dependable methods for inferring their distances," said lead author Burns.

"The quality of this data allows us to better correct our measurements to account for the dimming effect of cosmic dust" added Mark Phillips, an astronomer at Carnegie's Las Campanas Observatory in Chile and a co-author on the paper.

The calibration of these mile markers is crucially important, because there are disagreements between different methods for determining the universe's expansion rate. The Hubble constant can independently be estimated using the glow of background radiation left over from the Big Bang. This cosmic microwave background radiation has been measured with exquisite detail by the Planck satellite, and it gives astronomers a more slowly expanding universe than when measured using type Ia supernovae.

"This discrepancy could herald new physics, but only if it's real," Burns explained. "So, we need our type Ia supernova measurements to be as accurate as possible, but also to identify and quantify all sources of error."

Source: Carnegie Institution for Science [December 11, 2018]

Researchers have created tiny droplets of the ultra-hot matter that once filled the early universe, forming three distinct shapes and sizes: circles, ellipses and triangles.

Visualization of expanding drops of quark gluon plasmas in three geometric shapes [Credit: Javier Orjuela Koop]

The study, published in Nature Physics, stems from the work of an international team of scientists and focuses on a liquid-like state of matter called a quark gluon plasma. Physicists believe that this matter filled the entire universe during the first few microseconds after the Big Bang when the universe was still too hot for particles to come together to make atoms.

CU Boulder Professor Jamie Nagle and colleagues on an experiment known as PHENIX used a massive collider at Brookhaven National Laboratory in Upton, New York, to recreate that plasma. In a series of tests, the researchers smashed packets of protons and neutrons in different combinations into much bigger atomic nuclei.

They discovered that, by carefully controlling conditions, they could generate droplets of quark gluon plasma that expanded to form three different geometric patterns.

"Our experimental result has brought us much closer to answering the question of what is the smallest amount of early universe matter that can exist," Nagle said.

Researchers from CU Boulder and Vanderbilt University lead the data analysis efforts for the PHENIX experiment.

Scientists first started studying such matter at Brookhaven's Relativistic Heavy Ion Collider (RHIC) in 2000. They crashed together the heavy nuclei of gold atoms, generating temperatures of trillions of degrees Celsius. In the resulting boil, quarks and gluons, the subatomic particles that make up all protons and neutrons, broke free from their atomic chains and flowed almost freely.

Graphic showing how atomic collisions between different starting ingredients expand over time to produce plasmas in distinct shapes. The top collision was generated by slamming a single proton into a gold atom; the middle from a collision between a deuteron and a gold atom; and the bottom from a collision between helium-3 and a gold atom [Credit: PHENIX, Nature 2018]

Several years later, another group of researchers reported that they seemed to have created a quark gluon plasma not by slamming together two atoms, but by crashing together just two protons.

That was surprising because most scientists assumed that lone protons could not deliver enough energy to make anything that could flow like a fluid.

Nagle and his colleagues devised a way to test those results in 2014: If such tiny droplets behaved like liquid, then they should hold their shape.

As he explained, "Imagine that you have two droplets that are expanding into a vacuum. If the two droplets are really close together, then as they're expanding out, they run into each other and push against each other, and that's what creates this pattern."

In other words, if you toss two stones into a pond close together, the ripples from those impacts will flow into each other, forming a pattern that resembles an ellipse. The same could be true if you smashed a proton-neutron pair, called a deuteron, into something bigger, Nagle and Romatschke reasoned. Likewise, a proton-proton-neutron trio, also known as a helium-3 atom, might expand out into something akin to a triangle.

And that's exactly what the PHENIX experiment found: collisions of deuterons formed short-lasting ellipses, helium-3 atoms formed triangles and a single proton exploded in the shape of a circle.

The results, the researchers said, could help theorists better understand how the universe's original quark gluon plasma cooled over milliseconds, giving birth to the first atoms in existence.

The new study includes co-authors from 65 institutions. Co-authors from CU Boulder include postdoctoral researchers Ron Belmont and Darren McGlinchey and graduate student Javier Orjeula-Koop, all in physics.

Author: Daniel Strain | Source: University of Colorado at Boulder [December 10, 2018]

Scientists at the University of Oxford may have solved one of the biggest questions in modern physics, with a new paper unifying dark matter and dark energy into a single phenomenon: a fluid which possesses 'negative mass." If you were to push a negative mass, it would accelerate towards you. This astonishing new theory may also prove right a prediction that Einstein made 100 years ago.

3D illustration of the dark matter explosion and creation of the universe with billions of cosmic atoms, flying meteors, a lot of of light elements, and halos of new stars [Credit: Shutterstock]

Our current, widely recognised model of the Universe, called LambdaCDM, tells us nothing about what dark matter and dark energy are like physically. We only know about them because of the gravitational effects they have on other, observable matter.

This new model, published in Astronomy and Astrophysics, by Dr. Jamie Farnes from the Oxford e-Research Centre, Department of Engineering Science, offers a new explanation. Dr. Farnes says: "We now think that both dark matter and dark energy can be unified into a fluid which possesses a type of 'negative gravity," repelling all other material around them. Although this matter is peculiar to us, it suggests that our cosmos is symmetrical in both positive and negative qualities."

The existence of negative matter had previously been ruled out as it was thought this material would become less dense as the Universe expands, which runs contrary to our observations that show dark energy does not thin out over time. However, Dr. Farnes' research applies a 'creation tensor," which allows for negative masses to be continuously created. It demonstrates that when more and more negative masses are continually bursting into existence, this negative mass fluid does not dilute during the expansion of the cosmos. In fact, the fluid appears to be identical to dark energy.

Dr. Farnes's theory also provides the first correct predictions of the behaviour of dark matter halos. Most galaxies are rotating so rapidly they should be tearing themselves apart, which suggests that an invisible 'halo' of dark matter must be holding them together. The new research features a computer simulation of the properties of negative mass, which predicts the formation of dark matter halos just like the ones inferred by observations using modern radio telescopes.

Albert Einstein provided the first hint of the dark universe exactly 100 years ago, when he discovered a parameter in his equations known as the 'cosmological constant," which we now know to be synonymous with dark energy. Einstein famously called the cosmological constant his 'biggest blunder," although modern astrophysical observations prove that it is a real phenomenon. In notes dating back to 1918, Einstein described his cosmological constant, writing that 'a modification of the theory is required such that "empty space" takes the role of gravitating negative masses which are distributed all over the interstellar space." It is therefore possible that Einstein himself predicted a negative-mass-filled universe.

Dr. Farnes says: "Previous approaches to combining dark energy and dark matter have attempted to modify Einstein's theory of general relativity, which has turned out to be incredibly challenging. This new approach takes two old ideas that are known to be compatible with Einstein's theory—negative masses and matter creation—and combines them together.

"The outcome seems rather beautiful: dark energy and dark matter can be unified into a single substance, with both effects being simply explainable as positive mass matter surfing on a sea of negative masses."

Proof of Dr. Farnes's theory will come from tests performed with a cutting-edge radio telescope known as the Square Kilometre Array (SKA), an international endeavour to build the world's largest telescope in which the University of Oxford is collaborating.

Dr. Farnes adds: "There are still many theoretical issues and computational simulations to work through, and LambdaCDM has a nearly 30 year head start, but I'm looking forward to seeing whether this new extended version of LambdaCDM can accurately match other observational evidence of our cosmology. If real, it would suggest that the missing 95% of the cosmos had an aesthetic solution: we had forgotten to include a simple minus sign."

Source: University of Oxford [December 05, 2018]

A study led by Texas Tech University shows that supersoft X-ray emissions can come from accretion as well as nuclear fusion.

Credit: NASA/CXC/M.Weiss

For decades, astronomers and astrophysicists have used a specific type of supernova to measure the expansion of the universe. But a recent discovery led by Texas Tech University may turn that notion on its head.

Supersoft X-ray emission – a very strong level of the weakest X-rays – has long been considered a result of nuclear fusion on the surface of a white dwarf, a small, very dense star. But a new detection of supersoft emissions that are clearly not powered by fusion is showing scientists that fusion is not the only way such emissions occur, according to a study published in the journal Nature Astronomy.

The event, ASASSN16-oh, was first noticed as a transient in the Small Magellanic Cloud by the All-Sky Automated Survey. Additional observations from NASA's Swift Observatory and the Chandra X-ray Observatory helped to verify the finding.

"In the past, the supersoft sources have all been associated with nuclear fusion on the surface of white dwarfs," said lead author Tom Maccarone, a professor in the Texas Tech Department of Physics & Astronomy. "As a white dwarf captures material from a companion star, the material piles up on the surface and becomes hot, and, eventually nuclear fusion takes place, much like in a hydrogen bomb.

"But this emission is coming from a region smaller than the surface of the white dwarf, and we have strong arguments against any kind of explosion having taken place on the white dwarf. Specifically, there are no broad emission lines in the X-ray or optical spectra, so there cannot have been any kind of strong wind generated. In some cases, nuclear fusion can be steady on the surface of a white dwarf, but it cannot start immediately as steady fusion. There must be an explosion of some kind when the fusion starts."

The source of these emissions, then, is thought to be accretion – the process of accumulating matter – not fusion. The scientists believe the system consists of a highly evolved red giant star and a white dwarf with an extremely large disk of emission around it. The rate of inflow of matter through the disk is unstable, and when the material starts flowing more quickly, the brightness of the system shoots upward.

"What we're seeing here is a transient episode of supersoft emission, but without any of the signs that we associate with nuclear fusion," Maccarone said. "If a nova took place, we would expect to see material flowing away from the white dwarf. Here we don't. Instead, what we are seeing is hot emission from the disk that is transporting the material from the companion star to the white dwarf. The transfer of mass is happening at a higher rate than in any system we've caught in the past."

So what this finding shows is that there are two ways by which supersoft emission can be made: nuclear fusion and accretion.

"I am excited by this result," Maccarone said. "It was a totally new phenomenon, and any time one finds one of those, it's exciting."

As exciting as this finding is on its own, perhaps the most important part is that it may change how astrophysicists measure the expansion of the universe. These objects were thought to be one of the main ways by which white dwarfs grow in mass and eventually explode as Type Ia supernovae.

"These systems also are the way we measure the expansion of the universe," Maccarone said. "To measure that expansion more accurately than we do now, we need to understand the origin of the Type Ia supernovae. This finding – that there's a new way to make supersoft sources – will cause us to re-think our approach to matching up the populations of these objects with the rates of the supernovae."

Author: Glenys Young | Source: Texas Tech University [December 04, 2018]

Based on computer simulations and new observations from the Atacama Large Millimeter/submillimeter Array (ALMA), researchers have found that the rings of gas surrounding active supermassive black holes are not simple donut shapes. Instead, gas expelled from the center interacts with infalling gas to create a dynamic circulation pattern, similar to a water fountain in a city park.

ALMA image of the gas around the supermassive black hole in the center of the Circinus Galaxy. The distributions of CO molecular gas and C atomic gas are shown in orange and cyan, respectively [Credit: ALMA (ESO/NAOJ/NRAO), Izumi et al., 2018]

Most galaxies host a supermassive black hole, millions or billions of times as heavy as the Sun, in their centers. Some of these black holes swallow material quite actively. But astronomers have believed that rather than falling directly into the black hole, matter instead builds up around the active black hole forming a donut structure.

Takuma Izumi, a researcher at the National Astronomical Observatory of Japan (NAOJ), led a team of astronomers that used ALMA to observe the supermassive black hole in the Circinus Galaxy located 14 million light-years away from the Earth in the direction of the constellation Circinus. The team then compared their observations to a computer simulation of gas falling towards a black hole made with the Cray XC30 ATERUI supercomputer operated by NAOJ.

Artist’s impression of the gas motion around the supermassive black hole in the center of the Circinus Galaxy. The three  gaseous components form the long-theorized “donut” structure: (1) a disk of infalling dense cold molecular gas, (2) outflowing hot atomic gas, and (3) gas returning to the disk [Credit: NAOJ]

This comparison revealed that the presumptive "donut" is not actually a rigid structure, but instead a complex collection of highly dynamic gaseous components. First, cold molecular gas falling towards the black hole forms a disk near the plane of rotation. As it approaches the black hole, this gas is heated until the molecules break down into the component atoms and ions. Some of these atoms are then expelled above and below the disk, rather than being absorbed by the black hole. This hot atomic gas falls back onto the disk creating a turbulent three dimensional structure. These three components circulate continuously, similar to a water fountain in a city park.

"Previous theoretical models set a priori assumptions of rigid donuts," explains Keiichi Wada, a theoretician at Kagoshima University in Japan, who lead the simulation study and is a member of the research team. "Rather than starting from assumptions, our simulation started from the physical equations and showed for the first time that the gas circulation naturally forms a donut. Our simulation can also explain various observational features of the system."

Cross section of the gas around a supermassive black hole simulated with NAOJ’s supercomputer ATERUI. The different colors represent the density of the gas, and the arrows show the motion of the gas. It clearly shows  the three gaseous components forming the “donut” structure [Credit: Wada et al.]

"By investigating the motion and distribution of both the cold molecular gas and warm atomic gas with ALMA, we demonstrated the origin of the so-called 'donut' structure around active black holes," said Izumi. "Based on this discovery, we need to rewrite the astronomy textbooks."

The findings are published in The Astrophysical Journal.

Source: National Astronomical Observatory of Japan [November 30, 2018]

From their laboratories on a rocky planet dwarfed by the vastness of space, Clemson University scientists have managed to measure all of the starlight ever produced throughout the history of the observable universe.

Constructed using nine years of observations by Fermi’s Large Area Telescope, this map shows how the gamma-ray sky  appears at energies above 10 billion electron volts. The plane of our Milky Way galaxy runs along the middle of the plot.  Brighter colours indicate brighter gamma-ray sources [Credit: NASA/DOE/Fermi LAT Collaboration]

Astrophysicists believe that our universe, which is about 13.7 billion years old, began forming the first stars when it was a few hundred million years old. Since then, the universe has become a star-making tour de force. There are now about two trillion galaxies and a trillion-trillion stars. Using new methods of starlight measurement, Clemson College of Science astrophysicist Marco Ajello and his team analyzed data from NASA's Fermi Gamma-ray Space Telescope to determine the history of star formation over most of the universe's lifetime.

A collaborative paper titled "A gamma-ray determination of the Universe's star-formation history" was published in the journal Science and describes the results and ramifications of the team's new measurement process.

"From data collected by the Fermi telescope, we were able to measure the entire amount of starlight ever emitted. This has never been done before," said Ajello, who is lead author of the paper. "Most of this light is emitted by stars that live in galaxies. And so, this has allowed us to better understand the stellar-evolution process and gain captivating insights into how the universe produced its luminous content."

Putting a number on the amount of starlight ever produced has several variables that make it difficult to quantify in simple terms. But according to the new measurement, the number of photons (particles of visible light) that escaped into space after being emitted by stars translates to 4x10^84.

Or put another way: 4,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 photons.

Despite this stupendously large number, it is interesting to note that with the exception of the light that comes from our own sun and galaxy, the rest of the starlight that reaches Earth is exceedingly dim -- equivalent to a 60-watt light bulb viewed in complete darkness from about 2.5 miles away. This is because the universe is almost incomprehensibly huge. This is also why the sky is dark at night, other than light from the moon, visible stars and the faint glow of the Milky Way.


The Fermi Gamma-ray Space Telescope was launched into low orbit on June 11, 2008, and recently marked its 10-year anniversary. It is a powerful observatory that has provided enormous amounts of data on gamma rays (the most energetic form of light) and their interaction with the extragalactic background light (EBL), which is a cosmic fog composed of all the ultraviolet, visible and infrared light emitted by stars or from dust in their vicinity. Ajello and postdoctoral fellow Vaidehi Paliya analyzed almost nine years of data pertaining to gamma-ray signals from 739 blazars.

Blazars are galaxies containing supermassive black holes that are able to release narrowly collimated jets of energetic particles that leap out of their galaxies and streak across the cosmos at nearly the speed of light. When one of these jets happens to be pointed directly at Earth, it is detectable even when originating from extremely far away. Gamma ray photons produced within the jets eventually collide with the cosmic fog, leaving an observable imprint. This enabled Ajello's team to measure the density of the fog not just at a given place but also at a given time in the history of the universe.

"Gamma-ray photons traveling through a fog of starlight have a large probability of being absorbed," said Ajello, an assistant professor in the department of physics and astronomy. "By measuring how many photons have been absorbed, we were able to measure how thick the fog was and also measure, as a function of time, how much light there was in the entire range of wavelengths."

Using galaxy surveys, the star-formation history of the universe has been studied for decades. But one obstacle faced by previous research was that some galaxies were too far away, or too faint, for any present-day telescopes to detect. This forced scientists to estimate the starlight produced by these distant galaxies rather than directly record it.

Ajello's team was able to circumvent this by using Fermi's Large Area Telescope data to analyze the extragalactic background light. Starlight that escapes galaxies, including the most distant ones, eventually becomes part of the EBL. Therefore, accurate measurements of this cosmic fog, which have only recently become possible, eliminated the need to estimate light emissions from ultra-distant galaxies.

Paliya performed the gamma ray analysis of all 739 blazars, whose black holes are millions to billions of times more massive than our sun.


"By using blazars at different distances from us, we measured the total starlight at different time periods," said Paliya of the department of physics and astronomy. "We measured the total starlight of each epoch -- one billion years ago, two billion years ago, six billion years ago, etc. -- all the way back to when stars were first formed. This allowed us to reconstruct the EBL and determine the star-formation history of the universe in a more effective manner than had been achieved before."

When high-energy gamma rays collide with low-energy visible light, they transform into pairs of electrons and positrons. According to NASA, Fermi's ability to detect gamma rays across a wide range of energies makes it uniquely suited for mapping the cosmic fog. These particle interactions occur over immense cosmic distances, which enabled Ajello's group to probe deeper than ever into the universe's star-forming productivity.

"Scientists have tried to measure the EBL for a long time. However, very bright foregrounds like the zodiacal light (which is light scattered by dust in the solar system) rendered this measurement very challenging," said co-author Abhishek Desai, a graduate research assistant in the department of physics and astronomy. "Our technique is insensitive to any foreground and thus overcame these difficulties all at once."

Star formation, which occurs when dense regions of molecular clouds collapse and form stars, peaked around 11 billion years ago. But though the birthing of new stars has since slowed down, it has never stopped. For instance, about seven new stars are created in our Milky Way galaxy every year.

Establishing not only the present-day EBL, but revealing its evolution in cosmic history is a major breakthrough in this field, according to team member Dieter Hartmann, a professor in the department of physics and astronomy.

"Star formation is a great cosmic cycling and recycling of energy, matter and metals. It's the motor of the universe," Hartmann said. "Without the evolution of stars, we wouldn't have the fundamental elements necessary for the existence of life."

Understanding star formation also has ramifications for other areas of astronomical study, including research regarding cosmic dust, galaxy evolution and dark matter. The team's analysis will provide future missions with a guideline to explore the earliest days of stellar evolution -- such as the upcoming James Webb Space Telescope, which will be launched in 2021 and will enable scientists to hunt for the formation of primordial galaxies.

"The first billion years of our universe's history are a very interesting epoch that has not yet been probed by current satellites," Ajello concluded. "Our measurement allows us to peek inside it. Perhaps one day we will find a way to look all the way back to the Big Bang. This is our ultimate goal."

Source: Clemson University [November 29, 2018]

A supernova discovered by an international group of astronomers including Carnegie's Tom Holoien and Maria Drout, and led by University of Hawaii's Ben Shappee, provides an unprecedented look at the first moments of a violent stellar explosion. The light from the explosion's first hours showed an unexpected pattern, which Carnegie's Anthony Piro analyzed to reveal that the genesis of these phenomena is even more mysterious than previously thought.

The top left panel shows a color composite image of the galaxy in which the supernova occured, taken with the Pan-STARRS1 telescope on Haleakalā. The top middle panel is the "reference" image of the same galaxy, without the supernova emission, from the ASAS-SN survey, and the top right panel shows a similar image from NASA's Kepler Space Telescope. The bottom middle and right panels are the corresponding ASAS-SN and Kepler  images with the supernova. The bottom left panel is the difference between the two ASAS-SN images,  showing only the light from the supernova [Credit: Ben Shappee/ASASSN/NASA]

Type Ia supernovae are fundamental to our understanding of the cosmos. Their nuclear furnaces are crucial for generating many of the elements around us, and they are used as cosmic rulers to measure distances across the universe. Despite their importance, the actual mechanism that triggers a Type Ia supernova explosion has remained elusive for decades. That's why catching them in the act is crucial.

Astronomers have long tried to get detailed data at the initial moments of these explosions, with the hope of figuring out how these phenomena are triggered. This finally happened in February of this year with the discovery of a Type Ia supernova called ASASSN-18bt (also known as SN 2018oh).

ASASSN-18bt was discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN), an international network of telescopes headquartered at the Ohio State University that routinely scans the sky for supernovae and other cosmic explosions. NASA's Kepler space telescope was simultaneously able to take complementary data of this event. Kepler was designed to be incredibly sensitive to small changes in light for its mission of detecting extrasolar planets, so it was able to obtain especially detailed information about the explosion's genesis.

"ASASSN-18bt is the nearest and brightest supernova yet observed by Kepler, so it offered an excellent opportunity to test the predominant theories of supernova formation," said Shappee, who is lead author on the on the discovery and early time light curve paperand one of our Carnegie alumni.

Combining data from ASAS-SN, Kepler, and telescopes around the world, the astronomers realized that ASASSN-18bt looked unusual during its first couple of days.

"Many supernovae show a gradual increase in the light they put out," said Drout, who is jointly appointed at the University of Toronto. "But for this event, you could clearly see there's something unusual and exciting happening in the early times--an unexpected additional emission."

Type Ia supernovae originate from the thermonuclear explosion of a white dwarf star--the dead core left over by a Sun-like star after it exhausts its nuclear fuel. Material must be added to the white dwarf from a companion star to trigger the explosion, but the nature of the companion star and how the fuel is transferred has long been debated.

One possibility is that this additional light seen during the supernova's early times could be from the exploding white dwarf colliding with the companion star. Although this was the initial hypothesis, detailed comparisons with Piro's theoretical modeling work demonstrated that this additional light may have a different, unexplained origin.

"While the steep increase in ASASSN-18bt's early brightness could indicate that the explosion collides with another star, our follow-up data don't fit predictions for how this should look," Holoien said. "Other possibilities, such as an unusual distribution of radioactive material in the exploded star, are a better explanation for what we saw. More observations of ASASSN-18bt and more early discoveries like this one will hopefully help us differentiate between different models and better understand the origins of these explosions."

"Nature is always finding new ways to surprise us, and unique observations like this are great for motivating creative new approaches to how we think about these explosions, "added Piro. "As a theorist at the Carnegie Observatories, it's so helpful and inspiring to be right near the observers who are making these key measurements."

This supports a hypothesis put forward in recent work from the Carnegie Supernova Project, led by Maximilian Stritzinger ofAarhus University and co-led by Shappee and Piro, that there may be two distinct populations of Type Ia supernovae--those that show early emission and those that do not.

Thanks to ASAS-SN and the next generation of surveys that are now monitoring the sky every night, astronomers will find even more new supernovae and catch them at the moment of explosion. As more of these events are found and studied, they will hopefully home in on the solution to the longstanding mystery of how these stellar explosions originate.

Their findings are published in a trio of papers in The Astrophysical Journal and The Astrophysical Journal Letters [paper 1, paper 2, paper 3].

Source: Carnegie Institution for Science [November 29, 2018]

The Big Bang theory and the question of how life on Earth began has fascinated scientists for decades, but now new research from The University of Western Australia suggests the conditions that resulted from the Big Bang are different to what we thought.

Credit: Pasieka/Getty Images

The Big Bang theory, developed in 1927 is considered the most credible scientific explanation of how the universe was created. It suggests that through a process of expansion and explosion hydrogen gas was created which led to the formation of stars, and their death (supernova) led to the creation of life.

Researchers Professor Snezhana Abarzhi and Ms Annie Naveh from UWA's School of Mathematical Sciences conducted a mathematical analysis of the conditions that were created from a supernova.

Professor Abarzhi said although the supernova explosion was violent it wasn't as turbulent and quick as previously thought.

"It is traditionally considered that turbulence was the mechanism for energy transfer and accumulation which resulted in chemicals being formed in the supernova," Professor Abarzhi said.

"However our research has revealed it wasn't turbulent but actually a slow process where hot spots of energy were localised and trapped, resulting in the formation of, for example iron, gold and silver from atoms produced by the Big Bang.

"The findings are important because they challenge our understanding of the Big Bang theory and how life formed."

Professor Abarzhi said it was fascinating to see the complexity of how the universe might have been formed.

"Human beings essentially started as hydrogen atoms and energy, swirling around to create other chemicals and these interactions resulted in life," she said.

"The creation of life on Earth will always fascinate and challenge us, leaving more questions than answers, but this latest research brings us one step closer to understanding how we came to exist."

The findings are published in Proceedings of the National Academy of Sciences.

Source: University of Western Australia [November 27, 2018]

They are massive, they are very small, and they are extremely rare, but may hold the secrets of how galaxies form and evolve. A new study lifts the tip of the veil over the timid life of the massive ultra-compact galaxies. It was recently published in the journal Astronomy and Astrophysics and was carried out by an international team led by Fernando Buitrago, of Instituto de Astrofisica e Ciencias do Espaco (IA) and Faculdade de Ciencias da Universidade de Lisboa (FCUL).

Massive ultracompact galaxies with stellar masses greater than 80 billion suns [Credit: Buitrago et al., 2018]

Massive ultra-compact galaxies have several times more stars than our Milky Way, more than the equivalent to 80 billion suns, and thus are very bright, but their stars are densely packed within a size much smaller than our galaxy's. The researchers identified a new set of 29 galaxies with these properties, at distances between two and five billion light-years from Earth.

Seven of these shy heavyweights are actually primordial galaxies that remained untouched by others since their formation, more than ten billion years ago. These so-called relic galaxies open windows onto how galaxies looked like and were in the early ages of the universe, although they are in our galactic neighborhood.

"When you study very small objects and you study them in the far away universe, it is very hard to tell anything about them," says Fernando Buitrago. "As this sample of galaxies we studied is in the nearby universe and relatively close to us, even being truly small, we have a better chance of probing them."

One of the advances of the paper now published is to present the density of these massive ultra-compact galaxies in the universe, relics and non-relics altogether. The researchers have found only 29 in the most complete survey of galaxies in the local universe.

"They are so rare that we need roughly a volume with nearly 500 million light-years across to find a single one of them," says Ignacio Ferreras, the second author of the study.

Ferreras determined the ages of the stars in the galaxies, separating the redder and older relic galaxies from the bluer and younger. How could those relics be preserved untouched across cosmic time is something yet to be understood, says Fernando Buitrago.

According to the paradigm of galaxy formation and evolution, these relic ultra-compact galaxies could only be saved from merging with others and evolving by residing in overly populated clusters of galaxies. It may sound counter-intuitive as one would expect that in such crowded environments they would more easily interact and lose their original properties, but Buitrago explains: "In a place where there are many galaxies, there is also a lot of gravitational pull and the velocities of the galaxies are very high. Thus, the galaxies pass by each other without enough time to interact significantly."

"The surprise came when we realized that not all the galaxies in our sample live in such systems," Buitrago adds. "We found them in a range of environments, and for those that live in underdense neighborhoods, this is very hard to explain."

In this study, the researchers tried to measure some of the properties of these objects, such as their sizes and ages, but they are requesting observing time with large ground-based telescopes to point directly at them. In order to understand their past history, they would like to study in greater detail the places where they live in, the other galaxies around them, and their relative positions in space.

"Massive galaxies evolve in an accelerated way when compared to other galaxies in the universe. By understanding the properties of the most massive galaxies, we could understand the eventual fate of all the other galaxies, including our own Milky Way," Fernando Buitrago says.

Source: Instituto de Astrofísica e Ciências do Espaço [November 27, 2018]