Remarkable white dwarf star; coldest, dimmest ever detected

This is an artist impression of a white dwarf star in orbit with pulsar PSR J2222-0137. 

It may be the coolest and dimmest white dwarf ever identified. 

Credit: B. Saxton (NRAO /AUI /NSF)

A team of astronomers has identified possibly the coldest, faintest white dwarf star ever detected.

This ancient stellar remnant is so cool that its carbon has crystallized, forming an Earth-size diamond in space.

David Kaplan

"It's a really remarkable object," said David Kaplan, a professor at the University of Wisconsin-Milwaukee. "These things should be out there, but because they are so dim they are very hard to find."

Kaplan and his colleagues found this stellar gem using the National Radio Astronomy Observatory's (NRAO) Green Bank Telescope (GBT) and Very Long Baseline Array (VLBA), as well as other observatories.

White dwarfs are the extremely dense end-states of stars like our Sun that have collapsed to form an object approximately the size of the Earth.

Composed mostly of carbon and oxygen, white dwarfs slowly cool and fade over billions of years. The object in this new study is likely the same age as the Milky Way, approximately 11 billion years old.

Pulsars are rapidly spinning neutron stars, the superdense remains of massive stars that have exploded as supernovas.

As neutron stars spin, lighthouse-like beams of radio waves, streaming from the poles of its powerful magnetic field, sweep through space.

When one of these beams sweeps across the Earth, radio telescopes can capture the pulse of radio waves.

The pulsar companion to this white dwarf, dubbed PSR J2222-0137, was the first object in this system to be detected.

Jason Boyles

It was found using the GBT by Jason Boyles, then a graduate student at West Virginia University in Morgantown.

These first observations revealed that the pulsar was spinning more than 30 times each second and was gravitationally bound to a companion star, which was initially identified as either another neutron star or, more likely, an uncommonly cool white dwarf. The two were calculated to orbit each other once every 2.45 days.

The pulsar was then observed over a two-year period with the VLBA by Adam Deller, an astronomer at the Netherlands Institute for Radio Astronomy (ASTRON).

These observations pinpointed its location and distance from the Earth, approximately 900 light-years away in the direction of the constellation Aquarius.

This information was critical in refining the model used to time the arrival of the pulses at the Earth with the GBT.

By applying Einstein's theory of relatively, the researchers studied how the gravity of the companion warped space, causing delays in the radio signal as the pulsar passed behind it.

These delayed travel times helped the researchers determine the orientation of their orbit and the individual masses of the two stars.

The pulsar has a mass 1.2 times that of the Sun and the companion a mass 1.05 times that of the Sun.

These data strongly indicated that the pulsar companion could not have been a second neutron star; the orbits were too orderly for a second supernova to have taken place.

Knowing its location with such high precision and how bright a white dwarf should appear at that distance, the astronomers believed they should have been able to observe it in optical and infrared light.

Remarkably, neither the Southern Astrophysical Research (SOAR) telescope in Chile nor the 10-meter Keck telescope in Hawaii was able to detect it.

"Our final image should show us a companion 100 times fainter than any other white dwarf orbiting a neutron star and about 10 times fainter than any known white dwarf, but we don't see a thing," said Bart Dunlap, a graduate student at the University of North Carolina at Chapel Hill and one of the team members.

"If there's a white dwarf there, and there almost certainly is, it must be extremely cold."

The researchers calculated that the white dwarf would be no more than a comparatively cool 3,000 degrees Kelvin (2,700 degrees Celsius).

Astronomers believe that such a cool, collapsed star would be largely crystallized carbon, not unlike a diamond.

Other such stars have been identified and they are theoretically not that rare, but with a low intrinsic brightness, they can be deucedly difficult to detect.

Its fortuitous location in a binary system with a neutron star enabled the team to identify this one.

SOAR Telescope: A sharp eye on Southern binary stars

Click to view the animation demonstrating the orbit of the close binary pair Ba, Bb in the HIP 83716 Triple System. 

The orbit has been calculated from five observations (blue circles) taken between 2009, when the close binary was discovered at SOAR, and 2014, the date of the most recent observation. 

Animation Credit: M. A. Newhouse & NOAO/AURA/NSF

Unlike our sun, with its retinue of orbiting planets, many stars in the sky orbit around a second star.

These binary stars, with orbital periods ranging from days to centuries, have long been the primary tool for measuring basic quantities like the star's mass.

While masses of normal stars are now well determined, some binaries present special interest because their stars are unusual (e.g. very young) or because they may contain planets, gas clouds, or other stars.

Now, astronomers at the Cerro Tololo Inter-American Observatory (CTIO) and at the US Naval Observatory (USNO) are making use of the latest technology, speckle imaging, to measure the separation of close binary stars.

By observing them over a period of years, their obits have been determined with exquisite precision.

Using the new speckle camera at the 4.1-m Southern Astrophysical Research Telescope (SOAR) in Chile with its novel electron-multiplication CCD detector, the team is able to measure the angular separation of stars down to 25 milli arcseconds: this is equivalent to measuring the size of a quarter atop the Empire State building in New York - from Washington, DC.

This is over 2000 times better than the human eye can resolve. As Dr. Andrei Tokovinin, the lead author on the paper, said: "This camera surpasses adaptive-optics instruments at the 8-m telescopes, which work in the infrared and can only resolve binaries wider than 50 milli arcseconds."

The team, which includes astronomers from SOAR and from the USNO, has not only been observing previously known binary systems for which older data are very poor, but is also finding new double and multiple systems.

The attached animation shows the system HIP 83716, known to be double for over a century but until the SOAR camera examined it, nobody realized that the companion star was also a binary, making this a triple system.

The wide pair A,B orbit each other in about 520 years, while the newly discovered pair Ba, Bb orbit each other in just 6.5 years.

Over the past seven years, the speckle camera on SOAR has observed almost 2000 objects, both previously known and newly discovered binaries.

This is a unique dataset in terms of quantity and quality: prior to this project such measurements of southern binaries were made only occasionally by the team from the USNO.

More information: "Speckle Interferometry at SOAR in 2012 and 2013." Andrei Tokovinin, Brian D. Mason, and William I. Hartkopf, Andrei Tokovinin et al. 2014 The Astronomical Journal 147 123. DOI: 10.1088/0004-6256/147/5/123

Swiss Space Systems to Launch Robotic Mini-Shuttle in 2017

The Switzerland-based Swiss Space Systems announced plans to launch a privately built SOAR unmanned space plane from an Airbus A300 jetliner by 2017 for small satellite launches. 

CREDIT: Swiss Space Systems

A Swiss company has unveiled an ambitious plan to build a privately built robotic rocket plane by 2017 in order launch satellites into orbit.

The company Swiss Space Systems (S3) plans to loft the unmanned suborbital shuttle from the back of an Airbus A300 jetliner to serve as a commercial satellite launch platform.

The Payerne based, Switzerland firm unveiled the satellite launch concept on March 13 and is expected to reveal the supplier of its shuttle rocket engine in April.


"S3 aims to develop, build, certify and operate suborbital space shuttles dedicated to launching small satellites, enabling space access to be made more democratic thanks to an original system with launching costs up to four times less than at present," the company announced in a statement.

"The first test launches will be carried out by the end of 2017."

S3 officials said they plan to build a mock up of the unmanned mini-shuttle by 2014, then open the a commercial spaceport in Payerne in 2015.

The first flightworthy spacecraft prototype is slated to be built by in 2016, with the initial test flights following a year later. If all ges well, commercial satellite launches would begin in 2018.

Gregoire Loretan

The unmanned satellite launches may be just the beginning, S3 officials said.

"Our first priority is the launch of small satellites until 2018," Gregoire Loretan, S3's head of communications, told reporters.

"And the goal for S3 is to establish certification process and standards to help the development of manned flight afterwards."

This artist's illustration shows the Swiss Space Systems unmanned SOAR space plane gliding back to its spaceport after launching a small satellite. 

CREDIT: Swiss Space Systems A new rocket plane rises

According to S3's flight plan, the company plans to launch its robot rocket plane from an altitude of about 33,000 feet (10,000 meters). After separating from the carrier plane, the rocket plane will fire a liquid oxygen and kerosene rocket engine to reach an altitude of nearly 50 miles (80 kilometers).

S3 officials have dubbed the vehicle a space plane, though technically the rocket-powered craft will not fly high enough to cross the recognized the boundary of space, about 62 miles (100 km). But the 50-mile target altitude is high enough to launch a satellite into orbit.

At that height, the robotic shuttle will open its cargo bay doors to deploy a satellite equipped with its own rocket engine, a third stage, to launch the 550-pound (250 kilograms) satellite into an orbit about 434 miles (700 km) above Earth. The mini-shuttle should then glide back to Earth and land at its home spaceport.

The total development cost for the launch system is estimated to be about 200 million Swiss Francs, or $211 million. Another 50 million Francs ($53 million) will pay for a Swiss spaceport, S3 officials said.

"The overall budget is 250 millions [Swiss Francs], this includes one spaceport. A large part of this budget is already covered by private investors and our partners," Loretan said.