New Theories on Stellar Winds – Pulsating Magnetically Driven Radiative Energy

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A new study of the mechanism that drives stellar winds from the upper atmosphere of a star has shed new light. Astronomers think there are three possibilities: radiative, in which the pressure of the light pushes out the grains, magnetically driven, in which the stellar magnetic field plays a role in powering the flow, and pulsation driven, in which a periodic build-up of radiative energy in the stellar interior is suddenly released.

A new study of the mechanism that drives stellar winds from the upper atmosphere of a star has shed new light. Astronomers think there are three possibilities: radiative, in which the pressure of the light pushes out the grains, magnetically driven, in which the stellar magnetic field plays a role in powering the flow, and pulsation driven, in which a periodic build-up of radiative energy in the stellar interior is suddenly released.

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The winds of stars more evolved than the Sun (like the so-called giant stars that are cooler and larger in diameter than the Sun) often contain dust particles which enrich the interstellar medium with heavy elements. These winds also contain small grains on whose surfaces chemical reactions produce complex molecules. The dust also absorbs radiation and obscures visible light. Understanding the mechanism(s) that produce these winds in evolved stars is important both for modeling the wind and the character of the stellar environment, and for predicting the future evolution of the star.

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Nearly all stars have winds. The Sun’s wind, which originates from its hot outer layer (corona), contains charged particles emitted at a rate equivalent to about one-millionth of the moon’s mass each year. Some of these particles bombard the Earth, producing radio static, auroral glows, and (in extreme cases) disrupted global communications.

NASA'S Chandra Finds Fastest Wind From Stellar-Mass Black Hole
NASA’S Chandra Finds Fastest Wind From Stellar-Mass Black Hole

Over the years scientific opinion has varied among these alternatives, depending on each particular stellar example. Harvard–Smithsonian Center for Astrophysics Chris Johnson, and his colleagues explored the problem of wind-driving mechanism in giant stars by measuring the motion of the outflowing CO (carbon monoxide) gas around one the nearest and brightest giant stars, EU Del, which is only about 380 light-years away and shines with 1600 solar-luminosities.

new_equation 2012_m

New Equation:
Increase Charged Particles and Decreased Magnetic Field → Increase Outer Core Convection → Increase of Mantle Plumes → Increase in Earthquake and Volcanoes → Cools Mantle and Outer Core → Return of Outer Core Convection (Mitch Battros – July 2012)

Its radius, if the star were placed at the position of the Sun, would extend past the orbit of Venus. EU Del is known to be a semi-regular variable star which pulses every sixty days or so (but with some secondary periods as well), and infrared observations suggest it has a circumstellar dust shell.

The astronomers used the submillimeter APEX (Atacama Pathfinder Experiment) telescope to look at warm CO gas in the wind, making EU Del one of the first stars of its class to be studied with this relatively new tool. The team reports finding the CO moving at about ten kilometers per second (twenty two thousand miles per hour) with a total mass-loss rate equal to about the mass of the Moon each year.

Meteor Activity Outlook for April 9-15, 2016

During this period the moon reaches its first quarter phase on Thursday April 14th. On that date the moon will be located 90 degrees east of the Sun and will set during the mid-morning hours.
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This weekend the waxing crescent moon will set during the late evening hours and will not pose any problems for viewing meteor activity as long as you keep the lunar glare out of your field of view. The estimated total hourly meteor rates for evening observers this week is near 3 for observers located in the northern hemisphere and 4 for observers located south of the equator.

For morning observers the estimated total hourly rates should be near 8 as seen from mid-northern latitudes (45N) and 11 as seen from tropical southern locations (25S). The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity. Note that the hourly rates listed below are estimates as viewed from dark sky

sites away from urban light sources. Observers viewing from urban areas will see less activity as only the brightest meteors will be visible from such locations.

The radiant (the area of the sky where meteors appear to shoot from) positions and rates listed below are exact for Saturday night/Sunday morning April 9/10. These positions do not change greatly day to day so the listed coordinates may be used during this entire period. Most star atlases (available at science stores and planetariums) will provide maps with grid lines of the celestial coordinates so that you may find out exactly where these positions are located in the sky. A planisphere or computer planetarium program is also useful in showing the sky at any time of night on any date of the year.

Activity from each radiant is best seen when it is positioned highest in the sky, either due north or south along the meridian, depending on your latitude. It must be remembered that meteor activity is rarely seen at the radiant position. Rather they shoot outwards from the radiant so it is best to center your field of view so that the radiant lies at the edge and not the center. Viewing there will allow you to easily trace the path of each meteor back to the radiant (if it is a shower member) or in another direction if it is a sporadic.

Meteor activity is not seen from radiants that are located far below the horizon. The positions below are listed in a west to east manner in order of right ascension (celestial longitude). The positions listed first are located further west therefore are accessible earlier in the night while those listed further down the list rise later in the night.

These sources of meteoric activity are expected to be active this week.

The sigma Leonids (SLE) were first documented by Cuno Hoffmeister back in the 1940’s. Recent analysis show these meteors are active from April 8-25 with maximum activity occurring on the 15th. The radiant is currently located at 13:12 (198) +03. This area of the sky is actually located in central Virgo, 3 degrees east of the 3rd magnitude star known as Auva (delta Virginis).

I’m not certain why this source is called the Sigma Leonids as even Hoffmeister placed the radiant in central Virgo, far from the star known as sigma Leonis. Perhaps back then there was a source of activity thought to be in southeastern Leo active at the same time? This radiant is best placed near 0001 local Daylight Saving time when it lies highest above the horizon. Rates are currently less than 1 per hour and may approach 1 per hour at maximum. With an entry velocity of 19 km/sec., the average meteor from this source would be of slow velocity.

The center of the large Anthelion (ANT) radiant is currently located at 14:12 (213) -13. This position lies in southeastern Virgo, 3 degrees south of the faint star known as kappa Virginis. Due to the large size of this radiant, Anthelion activity may also appear from the nearby constellations of Libra, eastern Hydra, and Serpens Caput as well as Virgo. This radiant is best placed near 0200 local Daylight Saving time, when it lies on the meridian and is located highest in the sky. Rates at this time should be near 3 per hour no matter your location. With an entry velocity of 30 km/sec., the average Anthelion meteor would be of slow velocity.

The April rho Cygnids (AEC) were discovered by Dr. Peter Brown during his meteoroid stream survey using the Canadian Meteor Orbit Radar. These meteors are active from April 11-May 4 with maximum activity occurring on the 22nd. The radiant is currently located at 20:18 (304) +41. This area of the sky is located in central Cygnus, just 1 degree northwest of the 2nd magnitude star known as Sadr (gamma Cygni). This radiant is best placed during the last hour before dawn when it lies highest above the horizon in a dark sky. Current rates are expected to be less than 1 per hour. With an entry velocity of 42 km/sec., the average meteor from this source would be of medium velocity. Note that these meteors are synonymous with the Nu Cygnids (Molau and Rendtel, 2009).

The delta Aquiliids (DAL) were discovered by Dr. Peter Jenniskens and mentioned in his book “Meteor Showers and their Parent Comets”. Recent analysis show these meteors are active from April 7-13 with maximum activity occurring on the 9th. At maximum the radiant is located at 20:32 (308) +12. This area of the sky is actually located in central Delphinus just north of the 4th magnitude star known as Deneb Dulfim (epsilon Delphini). This radiant is best placed during the last hour before dawn when it lies highest above the horizon in a dark sky. Rates at maximum are expected to remain less than 1 per hour. With an entry velocity of 63 km/sec., the average meteor from this source would be of fast velocity.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately 5 sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near 2 per hour. As seen from the tropical southern latitudes (25S), morning rates would be near 8 per hour as seen from rural observing sites and 3 per hour during the evening hours. Locations between these two extremes would see activity between the listed figures.

 

BREAKING NEWS: Supernova Showered Earth with Radioactive Debris

An international team of scientists has found evidence of a series of massive supernova explosions near our solar system, which showered the Earth with radioactive debris. The scientists found radioactive iron-60 in sediment and crust samples taken from the Pacific, Atlantic and Indian Oceans.

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Some theories suggest cosmic rays from the supernova could have increased cloud cover. The scientists believe the supernova in this case were less than 300 light years away; close enough to be visible during the day and comparable to the brightness of the Moon.

The supernova explosions create many heavy elements and radioactive isotopes which are strewn into the cosmic neighborhood. Although Earth would have been exposed to an increased cosmic ray bombardment, the radiation would have been too weak to cause direct biological damage or trigger mass extinctions.

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Any iron-60 dating from the Earth’s formation more than four billion years ago has long since disappeared. The iron-60 atoms reached Earth in minuscule quantities and so the team needed extremely sensitive techniques to identify the interstellar iron atoms.

The team from Australia, the University of Vienna in Austria, Hebrew University in Israel, Shimizu Corporation and University of Tokyo, Nihon University and University of Tsukuba in Japan, Senckenberg Collections of Natural History Dresden and Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany, also found evidence of iron-60 from an older supernova around eight million years ago, coinciding with global faunal changes in the late Miocene.

supernova_nedir

The iron-60 was concentrated in a period between 3.2 and 1.7 million years ago, which is relatively recent in astronomical terms, said research leader Dr Anton Wallner from The Australian National University (ANU).

“We were very surprised that there was debris clearly spread across 1.5 million years,” said Dr Wallner, a nuclear physicist in the ANU Research School of Physics and Engineering. “It suggests there were a series of supernova, one after another. “It’s an interesting coincidence that they correspond with when the Earth cooled and moved from the Pliocene into the Pleistocene period.”

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The dating showed the fallout had only occurred in two time periods, 3.2 to 1.7 million years ago and eight million years ago. Current results from TU Munich are in line with these findings.

A possible source of the supernova is an ageing star cluster, which has since moved away from Earth, independent work led by TU Berlin has proposed in a parallel publication. The cluster has no large stars left, suggesting they have already exploded as supernova, throwing out waves of debris.

New Study Shows How Black Holes and Galaxies Formed

Until recently, many researchers thought supermassive black holes were seeded by the collapse of some of the first stars. But modeling work by several groups has suggested that this process would only lead to small black holes.

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Kentaro Nagamine at Osaka University’s Department of Earth and Space Science, Isaac Shlosman at the University of Kentucky and co-workers simulated a different situation, in which supermassive black holes are seeded by clouds of gas falling into potential wells created by dark matter – the invisible matter that astronomers believe makes up 85% of the mass of the Universe.

Simulating the dynamics of huge gas clouds is extremely complex, so the team had to use some numerical tricks called ‘sink particles’ to simplify the problem.

“Although we have access to extremely powerful supercomputers at Osaka University’s Cybermedia Center and the National Astronomical Observatory of Japan, we can’t simulate every single gas particle,” explains Nagamine. “Instead, we model small spatial scales using sink particles, which grow as the surrounding gas evolves. This allows us to simulate much longer timescales than was previously possible.”

The researchers found that most seed particles in their simulations did not grow very much, except for one central seed, which grew rapidly to more than 2 million Sun-masses in just 2 million years, representing a feasible path toward a supermassive black hole. Moreover, as the gas spun and collapsed around the central seed it formed two misaligned accretion discs, which have never been observed before.

In other recent work, Nagamine and co-workers described the growth of massive galaxies that formed around the same time as supermassive black holes. “We like to push the frontier of how far back in time we can see,” says Nagamine. The researchers hope their simulations will be validated by real data when NASA’s James Webb Space Telescope, due to be launched in 2018, observes distant sources where direct gas collapse is happening.

Chemistry of Star and Planet Formation

In the last two decades, humanity has discovered thousands of extrasolar planetary systems. Recent studies of star- and planet-formation have shown that chemistry plays a pivotal role in both shaping these systems and delivering water and organic species to the surfaces of nascent terrestrial planets. Professor Geoffrey A. Blake in Chemical Engineering at the California Institute of Technology talked to Duke faculty and students over late-afternoon pizza in the Physics building on the role of chemistry in star and planet formation and finding other Earth-like planets.

chemistry of stars

In the late 18th century, French scholar Pierre-Simon Laplace analyzed what our solar system could tell us about the formation & evolution of planetary systems. Since then, scientists have used the combination our knowledge for small bodies – asteroids – and large bodies – planets – to figure out how solar systems and planets are formed.

In 2015, Professor Blake and other researchers investigated more into ingredients in planets necessary for the development of life.
Using the Earth and our solar system as the basis for their data, they explored the relative disposition of carbon and nitrogen in each stage of star and planet formation to learn more about core formation and atmospheric escape. Analyzing the carbon-silicon atomic ratio in planets and comets, Professor Blake discovered that rocky bodies in the solar system are generally carbon-poor. Since carbon is essential for our survival, however, Blake needed to determine the range of carbon content that terrestrial planets can have and still have active biosystem.

With the Kepler mission, scientists have detected a variety of planetary objects in the universe. How many of these star-planet systems – based on measured distributions – have ‘solar system’ like outcomes? A “solar system” like planetary system has at least one Earth-like planet at approximately 1 astronomical unit (AU) from the star – where more ideal conditions for life can develop – and at least one ice giant like Jupiter at 3-5 AU in order to keep away comets from the Earth-like planet. In our galaxy alone, there are around 10 billion stars and at least 10 million planets. For those stars similar to our sun, there exist over 4 million planetary systems similar to our solar system, with the closest Earth-like planet at 20 light years away. With the rapid improvement of scientific knowledge and technology, Professor Blake estimates that we would be able to collect evidence within next 5-6 years of planets within 40-50 light years to determine if they have a habitable atmosphere.

How does an Earth and a Jupiter form at their ideal distances from a star? Let’s take a closer look at how stars and planets are created – via the astrochemical cycle. Essentially, dense clouds of gas and dust become so opaque and cold that they collapse into a disk. The disk, rotating around a to-be star, begins to transport mass in toward the center and angular momentum outward. Then, approximately 1% of the star mass is left over from the process, which is enough to form planets. This is also why planets around stars are ubiquitous.

How are the planets formed? The dust grains unused by the star collide and grow, forming larger particles at specific distances from the star – called snowlines – where water vapor turns into ice and solidifies. These “dust bunnies” grow into planetesimals (~10-50 km diameter), such as asteroids and comets. If the force of gravity is large enough, the planetesimals increase further in size to form oligarchs (~0.1-10 times the mass of the Earth), that then become the large planets of the solar system.

In our solar system, a process called dynamic reorganization occurred that restructured the order of our planets, putting Uranus before Neptune. This means that if other solar systems did not undergo such dynamic reorganization at an early point in formation of solar system, then other Earths may have lower organic and water content than our Earth. In that case, what constraints do we need to apply to determine if a water/organic delivery mechanism exists for exo-Earths? Although we do not currently have the scientific knowledge to answer this, with ALMA and the next generation of optical/IR telescopes, we will be able image the birth of solar systems directly and better understand how our universe came to be.

To the chemistry students at Duke, Professor Blake relayed an important message: learn chemistry fundamentals very carefully while in college. Over the next 40-50 years, your interests will change gears many times. Strong fundamentals, however, will serve you well, since you are now equipped to learn in many different areas and careers.

INTEGRAL Sets Limits on Gamma Rays from Merging Black Holes

The terrestrial Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves – fluctuations in the fabric of space-time – produced by a pair of black holes as they spiraled towards each other before merging. The signal lasted less than half a second.

gravitational waves

The discovery was the first direct observation of gravitational waves, predicted by Albert Einstein a century ago.

Two days after the detection, the LIGO team alerted a number of ground- and space-based astronomical facilities to look for a possible counterpart to the source of gravitational waves. The nature of the source was unclear at the time, and it was hoped that follow-up observations across the electromagnetic spectrum might provide valuable information about the culprit.

Gravitational waves are released when massive bodies are accelerated, and strong emission should occur when dense stellar remnants such as neutron stars or black holes spiral towards each other before coalescing.

Models predict that the merging of two stellar-mass black holes would not produce light at any wavelength, but if one or two neutron stars were involved in the process, then a characteristic signature should be observable across the electromagnetic spectrum.

Another possible source of gravitational waves would be an asymmetric supernova explosion, also known to emit light over a range of wavelengths.
It was not possible to pinpoint the LIGO source – its position could only be narrowed down to a very long strip across the sky.

Observatories searched their archives in case data had been serendipitously collected anywhere along this strip around the time of the gravitational wave detection. They were also asked to point their telescopes to the same region in search for any possible ‘afterglow’ emission.

INTEGRAL is sensitive to transient sources of high-energy emission over the whole sky, and thus a team of scientists searched through its data, seeking signs of a sudden burst of hard X-rays or gamma rays that might have been recorded at the same time as the gravitational waves were detected.

“We searched through all the available INTEGRAL data, but did not find any indication of high-energy emission associated with the LIGO detection,” says Volodymyr Savchenko of the François Arago Centre in Paris, France. Volodymyr is the lead author of a paper reporting the results, published today in Astrophysical Journal Letters.

The team analysed data from the Anti-Coincidence Shield on INTEGRAL’s SPI instrument. The shield helps to screen out radiation and particles coming from directions other than that where the instrument is pointing, as well as to detect transient high-energy sources across the whole sky.

The team also looked at data from INTEGRAL’s IBIS instrument, although at the time it was not pointing at the strip where the source of gravitational waves was thought to be located.

“The source detected by LIGO released a huge amount of energy in gravitational waves, and the limits set by the INTEGRAL data on a possible simultaneous emission of gamma rays are one million times lower than that,” says co-author Carlo Ferrigno from the INTEGRAL Science Data Center at the University of Geneva, Switzerland.

Subsequent analysis of the LIGO data has shown that the gravitational waves were produced by a pair of coalescing black holes, each with a mass roughly 30 times that of our Sun, located about 1.3 billion light years away. Scientists do not expect to see any significant emission of light at any wavelength from such events, and thus INTEGRAL’s null detection is consistent with this scenario.

Similarly, nothing was seen by the great majority of the other astronomical facilities making observations from radio and infrared to optical and X-ray wavelengths.

The only exception was the Gamma-Ray Burst Monitor on NASA’s Fermi Gamma-Ray Space Telescope, which observed what appears to be a sudden burst of gamma rays about 0.4 seconds after the gravitational waves were detected. The burst lasted about one second and came from a region of the sky that overlaps with the strip identified by LIGO.

This detection sparked a bounty of theoretical investigations, proposing possible scenarios in which two merging black holes of stellar mass could indeed have released gamma rays along with the gravitational waves.

However, if this gamma-ray flare had had a cosmic origin, either linked to the LIGO gravitational wave source or to any other astrophysical phenomenon in the Universe, it should have been detected by INTEGRAL as well. The absence of any such detection by both instruments on INTEGRAL suggests that the measurement from Fermi could be unrelated to the gravitational wave detection.

“This result highlights the importance of synergies between scientists and observing facilities worldwide in the quest for as many cosmic messengers as possible, from the recently-detected gravitational waves to particles and light across the spectrum,” says Erik Kuulkers, INTEGRAL Project Scientist at ESA.

This will become even more important when it becomes possible to observe gravitational waves from space. This has been identified as the goal for the L3 mission in ESA’s Cosmic Vision program, and the technology for building it is currently being tested in space by ESA’s LISA Pathfinder mission.

Such an observatory will be capable of detecting gravitational waves from the merging of supermassive black holes in the centers of galaxies for months prior to the final coalescence, making it possible to locate the source much more accurately and thus provide astronomical observatories with a place and a time to look out for associated electromagnetic emission.

“We are looking forward to further collaborations and discoveries in the newly-inaugurated era of gravitational astronomy,” concludes Erik.

Journey to the Center of Our Galaxy

Peering deep into the heart of our home galaxy, the Milky Way, the NASA/ESA Hubble Space Telescope reveals a rich tapestry of more than half a million stars. Apart from a few, blue, foreground stars, almost all of the stars pictured in the image are members of the Milky Way nuclear star cluster, the densest and most massive star cluster in the galaxy. Hidden in the center of this cluster is the Milky Way’s resident supermassive black hole.

Milky Way nuclear star cluster

The center of the Milky Way, 27 000 light-years away in the constellation of Sagittarius, is a crowded place. This region is so tightly packed that it is equivalent to having one million stars crammed into the volume of space between us and Alpha Centauri, located 4.3 light-years away. At the very hub of our galaxy, this dense nuclear star cluster surrounds the Milky Way’s central supermassive black hole, known as Sagittarius A*, which alone is about four million times the mass of the Sun.

Sagittarius A* is not the only mystery lurking in this part of the galaxy. The crowded center contains numerous objects that are hidden at visible wavelengths by thick clouds of dust in the galaxy’s disc. In order to truly understand the central part of our galaxy astronomers used the infrared vision of Hubble to peer through this obscuring dust. To reveal the image in all its glory the scientists then assigned visible colors to the different wavelengths of infrared light, which is invisible to human eyes.

The blue stars in the image are foreground stars, which are closer to Earth than the nuclear star cluster, whilst the red stars are either behind much more intervening dust, or are embedded in dust themselves. Some extremely dense clouds of gas and dust are seen in silhouette, appearing dark against the bright background stars. These clouds are so thick that even Hubble’s infrared capability cannot penetrate them. In addition to the stars hidden by the dust astronomers estimate that there are about 10 million stars in the cluster which are too faint to see, even for Hubble.

Using Hubble’s vantage point above the atmosphere and its high resolution, astronomers were able not only to reveal the stars in this cluster but also to measure their movements over a period of four years.

Using this information, they inferred important properties of the nuclear star cluster, such as its mass and structure. The motion of the stars may also offer astronomers a glimpse into how the nuclear star cluster was formed—whether it was built up over time from globular star clusters that happened to fall into the center of the galaxy, or from gas spiraling in from the Milky Way’s disc to form stars at the core.