ESO: White dwarf star blasts particle beam at companion red dwarf

ESO (European Southern Observatory) released this report today about an unusual star system first observed by a group of amateur astronomers:

White Dwarf Lashes Red Dwarf with Mystery Ray

Astronomers using ESO’s Very Large Telescope, along with other telescopes on the ground and in space, have discovered a new type of exotic binary star. In the system AR Scorpii a rapidly spinning white dwarf star powers electrons up to almost the speed of light. These high energy particles release blasts of radiation that lash the companion red dwarf star, and cause the entire system to pulse dramatically every 1.97 minutes with radiation ranging from the ultraviolet to radio. The research will be published in the journal Nature on 28 July 2016.

This artist’s impression shows the strange object AR Scorpii. In this unique double star a rapidly spinning white dwarf star (right) powers electrons up to almost the speed of light. These high energy particles release blasts of radiation that lash the companion red dwarf star (left) and cause the entire system to pulse dramatically every 1.97 minutes with radiation ranging from the ultraviolet to radio.
This artist’s impression shows the strange object AR Scorpii. In this unique double star a rapidly spinning white dwarf star (right) powers electrons up to almost the speed of light. These high energy particles release blasts of radiation that lash the companion red dwarf star (left) and cause the entire system to pulse dramatically every 1.97 minutes with radiation ranging from the ultraviolet to radio. Larger image

In May 2015, a group of amateur astronomers from Germany, Belgium and the UK came across a star system that was exhibiting behaviour unlike anything they had ever encountered. Follow-up observations led by the University of Warwick and using a multitude of telescopes on the ground and in space [1], have now revealed the true nature of this previously misidentified system.

The star system AR Scorpii, or AR Sco for short, lies in the constellation of Scorpius, 380 light-years from Earth. It comprises a rapidly spinning white dwarf [2], the size of Earth but containing 200 000 times more mass, and a cool red dwarf companion one third the mass of the Sun [3], orbiting one another every 3.6 hours in a cosmic dance as regular as clockwork.

This artist’s impression video shows the strange object AR Scorpii. In this unique double star a rapidly spinning white dwarf star powers electrons up to almost the speed of light. These high energy particles release blasts of radiation that lash the companion red dwarf star and cause the entire system to pulse dramatically every 1.97 minutes with radiation ranging from the ultraviolet to radio. Credit: ESO/L. Calçada/University of Warwick

In a unique twist, this binary star system is exhibiting some brutal behaviour. Highly magnetic and spinning rapidly, AR Sco’s white dwarf accelerates electrons up to almost the speed of light. As these high energy particles whip through space, they release radiation in a lighthouse-like beam which lashes across the face of the cool red dwarf star, causing the entire system to brighten and fade dramatically every 1.97 minutes. These powerful pulses include radiation at radio frequencies, which has never been detected before from a white dwarf system.

This wide-field image from the Digitized Sky Survey 2 shows the rich starfields surrounding the exotic binary star system AR Scorpii.
This wide-field image from the Digitized Sky Survey 2 shows the rich starfields surrounding the exotic binary star system AR Scorpii.

Lead researcher Tom Marsh of the University of Warwick’s Astrophysics Group commented:

AR Scorpii was discovered over 40 years ago, but its true nature was not suspected until we started observing it in 2015. We realised we were seeing something extraordinary within minutes of starting the observations.”

The observed properties of AR Sco are unique. They are also mysterious. The radiation across a broad range of frequencies is indicative of emission from electrons accelerated in magnetic fields, which can be explained by AR Sco’s spinning white dwarf. The source of the electrons themselves, however, is a major mystery — it is not clear whether it is associated with the white dwarf itself, or its cooler companion.

AR Scorpii was first observed in the early 1970s and regular fluctuations in brightness every 3.6 hours led it to be incorrectly classified as a lone variable star [4]. The true source of AR Scorpii’s varying luminosity was revealed thanks to the combined efforts of amateur and professional astronomers. Similar pulsing behaviour has been observed before, but from neutron stars — some of the densest celestial objects known in the Universe  — rather than white dwarfs.

Boris Gänsicke, co-author of the new study, also at the University of Warwick, concludes:

We’ve known pulsing neutron stars for nearly fifty years, and some theories predicted white dwarfs could show similar behaviour. It’s very exciting that we have discovered such a system, and it has been a fantastic example of amateur astronomers and academics working together.

This chart shows the location of the exotic binary star AR Scorpii in the bright constellation of Scorpius (The Scorpion). The stars visible with the naked eye on a dark clear night are shown and the location of AR Scorpii marked with a red circle.
This chart shows the location of the exotic binary star AR Scorpii in the bright constellation of Scorpius (The Scorpion). The stars visible with the naked eye on a dark clear night are shown and the location of AR Scorpii marked with a red circle.

Notes

[1] The observations underlying this research were carried out on: ESO’s Very Large Telescope (VLT) located at Cerro Paranal, Chile; the William Herschel and Isaac Newton Telescopes of the Isaac Newton Group of telescopes sited on the Spanish island of La Palma in the Canaries; the Australia Telescope Compact Array at the Paul Wild Observatory, Narrabri, Australia; the NASA/ESA Hubble Space Telescope; and NASA’s Swift satellite.

[2]  White dwarfs form late in the life cycles of stars with masses up to about eight times that of our Sun. After hydrogen fusion in a star’s core is exhausted, the internal changes are reflected in a dramatic expansion into a red giant, followed by a contraction accompanied by the star’s outer layers being blown off in great clouds of dust and gas. Left behind is a white dwarf, Earth-sized but 200 000 times more dense. A single spoonful of the matter making up a white dwarf would weigh about as much as an elephant here on Earth.

[3] This red dwarf is an M type star. M type stars are the most common class in the Harvard classification system, which uses single letters to group stars according their spectral characteristics. The famously awkward to remember sequence of classes runs: OBAFGKM, and is often remembered using the mnemonic Oh Be A Fine Girl/Guy, Kiss Me.

[4] A variable star is one whose brightness fluctuates as seen from Earth. The fluctuations may be due to the intrinsic properties of the star itself changing. For instance some stars noticeably expand and contract. It could also be due to another object regularly eclipsing the star. AR Scorpii was mistaken for a single variable star as the orbiting of two stars also results in regular fluctuations in observed brightness.

Dawn: What happened to the large craters on Ceres?

The Dawn probe orbiting the dwarf planet Ceres in the Asteroid Belt has returned detailed imagery of the surface. So small features can now be studied but one mystery that has arisen is the absence of large craters. Somehow such craters have disappeared due to “Ceres’ peculiar composition and internal evolution”:

The Case of the Missing Ceres Craters

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Scientists with NASA’s Dawn mission were surprised to find that Ceres has no clear signs of truly giant impact basins. This image shows both visible (left) and topographic (right) mapping data from Dawn. Credit: NASA/JPL-Caltech/SwRI – Larger image.
Ceres is covered in countless small, young craters, but none are larger than 175 miles (280 kilometers) in diameter. To scientists, this is a huge mystery, given that the dwarf planet must have been hit by numerous large asteroids during its 4.5 billion-year lifetime. Where did all the large craters go?

A new study in the journal Nature Communications explores this puzzle of Ceres’ missing large craters, using data from NASA’s Dawn spacecraft, which has been orbiting Ceres since March 2015.

“We concluded that a significant population of large craters on Ceres has been obliterated beyond recognition over geological time scales, which is likely the result of Ceres’ peculiar composition and internal evolution,” said lead investigator Simone Marchi, a senior research scientist at the Southwest Research Institute in Boulder, Colorado. 

Marchi and colleagues modeled collisions of other bodies with Ceres since the dwarf planet formed, and predicted the number of large craters that should have been present on its surface. These models predicted Ceres should have up to 10 to 15 craters larger than 250 miles (400 kilometers) in diameter, and at least 40 craters larger than 60 miles (100 kilometers) wide. However, Dawn has shown that Ceres has only 16 craters larger than 60 miles, and none larger than 175 miles (280 kilometers) across.

One idea about Ceres’ origins holds that it formed farther out in the solar system, perhaps in the vicinity of Neptune, but migrated in to its present location. However, scientists determined that even if Ceres migrated into the main asteroid belt relatively late in solar system history, it should still have a significant number of large craters.

“Whatever the process or processes were, this obliteration of large craters must have occurred over several hundred millions of years,” Marchi said.

Dawn’s images of Ceres reveal that the dwarf planet has at least three large-scale depressions called “planitiae” that are up to 500 miles (800 kilometers) wide. These planitiae have craters in them that formed in more recent times, but the larger depressions could be left over from bigger impacts. One of them, called Vendimia Planitia, is a sprawling area just north of Kerwan crater, Ceres’ largest well-defined impact basin. Vendimia Planitia must have formed much earlier than Kerwan.

One reason for the lack of large craters could be related the interior structure of Ceres. There is evidence from Dawn that the upper layers of Ceres contain ice. Because ice is less dense than rock, the topography could “relax,” or smooth out, more quickly if ice or another lower-density material, such as salt, dominates the subsurface composition. Recent analysis of the center of Ceres’ Occator Crater suggests that the salts found there could be remnants of a frozen ocean under the surface, and that liquid water could have been present in Ceres’ interior.

Past hydrothermal activity, which may have influenced the salts rising to the surface at Occator, could also have something to do with the erasure of craters. If Ceres had widespread cryovolcanic activity in the past — the eruption of volatiles such as water — these cryogenic materials also could have flowed across the surface, possibly burying pre-existing large craters. Smaller impacts would have then created new craters on the resurfaced area.

“Somehow Ceres has healed its largest impact scars and renewed old, cratered surfaces,” Marchi said.

Ceres differs from Dawn’s previous destination, protoplanet Vesta, in terms of cratering. Although Vesta is only half the size of Ceres, it has a well-preserved 300-mile- (500-kilometer) -wide crater called Rheasilvia, where an impacting asteroid knocked out a huge chunk of the body. This and other large craters suggest that Vesta has not had processes at work to smooth its surface, perhaps because it is thought to have much less ice. Dawn visited Vesta for 14 months from 2011 to 2012.

“The ability to compare these two very different worlds in the asteroid belt — Vesta and Ceres — is one of the great strengths of the Dawn mission,” Marchi said.

Dawn’s mission is managed by JPL for NASA’s Science Mission Directorate in Washington. Dawn is a project of the directorate’s Discovery Program, managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team. For a complete list of mission participants, visit: dawn.jpl.nasa.gov/mission

More information about Dawn is available at the following sites:

Videos: Nexø I launch review + ULA/Ball Aerospace interns launch 50 ft rocket

Here’s a short video showing highlights of the Nexø I launch and recovery by Copenhagen Suborbitals  on Saturday (see earlier posting):

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On Sunday, interns at United Launch Alliance (ULA) and Ball Aerospace in Colorado flew a 50 foot (15.24 m) rocket that they built this summer. The “Future Heavy” rocket carried 16 payloads developed by interns and students as well.

Here is a press release about the launch: United Launch Alliance and Ball Aerospace Interns, Colorado Students Participate in Record-setting – ULA –

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The Space Show this week – July.25.2016

The guests and topics of discussion on The Space Show this week:

1. Monday, July25 , 2016: 2-3:30 PM PDT (5-6:30 PM EDT, 4-5:30 PM CDT): We welcome DR. RISHABH MAHARAJA to the program to discuss the Hermes Project.

2. Tuesday, July 26, 2016: 7-8:30 PM PDT (10-11:30 PM EDT, 9-10:30 PM CDT) We welcome back DR. PAT PATTERSON to discuss the SmallSat Conference for this year. Visit www.smallsat.org.

3. Friday, July 29, 2016: 2016; 9:30-11AM PDT; (12:30-2 PM EDT; 11:30 AM – 1 PM CDT) We welcome back DR. ERIK SEEDHOUSE with some of his students for a special Space Show program.

4. Sunday, July 31, 2016: 12-1:30 PM PDT (3-4:30 PM EDT, 2-3:30 PM CDT): OPEN LINES. First time callers are welcome. All topics regarding space and STEM issues are welcome.

See also:
* The Space Show on Vimeo – webinar videos
* The Space Show’s Blog – summaries of interviews.
* The Space Show Classroom Blog – tutorial programs

The Space Show is a project of the One Giant Leap Foundation.

Copenhagen Suborbitals Nexø I rocket launches with mixed results

Yesterday Copenhagen Suborbitals launched their rocket Nexø I, their most advanced vehicle yet, from a floating platform in the Baltic Sea. (See earlier posting). The good news is that the rocket lifted off successfully with its liquid-fueled engine (Ethanol and Liquid Oxygen) and active guidance system and was successfully recovered. The bad news is that it failed to reach its planned altitude and the parachute system failed to open: The Nexø I rocket launched – Copenhagen Suborbitals –

It was a beautiful launch with a not so great landing. The rocket flew to about 1514 meters before a catastrophic failure occurred.

Even though it didn’t go completely as planed we still see it as a partially success. A lot of sub systems actually work as they should.

Nexø-1 Rocket liftoff

We managed to recover the rocket. We will therefore have a good chance of finding the root cause of the failure.

We will post more about the launch and crash after we have had a closer look at the rocket and telemetry data.

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Here is a video of the webcast. The countdown to liftoff starts at the 3 hr 20 min 8 sec mark:

Today there is some preliminary analysis: Preliminary impressions from Nexø I flight event. – Copenhagen Suborbitals

We have not yet had opportunity to examine data, parts or footage.

A tentative speculation on root cause would be simple LOX [Liquid Oxygen] overload. In other words a problem with measuring the correct amount of LOX in the tank, which we have encountered previously, and worked on solving via several methods. We will look into this.

Too much LOX will result in a too small gas pocket in the tank – which equals too little gas propellant energy and a premature loss of tank pressure in the LOX tank, again resulting in an increasing O/F-ratio mismatch. The engine subsequently extinguished.

The GNC didn’t detect acceleration below minimum, as this detection was removed from the algorithm prior to the mission, based on the fact that the acceleration, through the use of pressure blow-down at relatively low altitude, would be very low before the occurrence of MECO.

The GNC instead used the chamber pressure. This was low at an unusually early time. The GNC treated this as a sensor failure, and instead an estimated pressure, based on a table generated from earlier tests, was used.

Thus the GNC didn’t signal the deployment of the parachute, as it was under the (false) impression that the engine was still operating as expected.