Hubble finds supernova companion star after two decades

This is an artist’s impression of supernova 1993J, which exploded in the galaxy M81. 

Using the Hubble Space Telescope, astronomers have identified the blue helium-burning companion star, seen at the center of the expanding nebula of debris from the supernova. 

Credit: NASA, ESA, G. Bacon (STScI)

Using NASA's Hubble Space Telescope, astronomers have discovered a companion star to a rare type of supernova.

The discovery confirms a long-held theory that the supernova, dubbed supernova 1993J, occurred inside what is called a binary system, where two interacting stars caused a cosmic explosion.

"This is like a crime scene, and we finally identified the robber," said Alex Filippenko, professor of astronomy at University of California (UC) at Berkeley.

"The companion star stole a bunch of hydrogen before the primary star exploded."

SN 1993J is an example of a Type IIb supernova, unusual stellar explosions that contains much less hydrogen than found in a typical supernova.

Astronomers believe the companion star took most of the hydrogen surrounding the exploding main star and continued to burn as a super-hot helium star.

"A binary system is likely required to lose the majority of the primary star's hydrogen envelope prior to the explosion."

"The problem is that, to date, direct observations of the predicted binary companion star have been difficult to obtain since it is so faint relative to the supernova itself," said lead researcher Ori Fox of UC Berkeley.

SN 1993J resides in the Messier M81 galaxy, about 11 million light-years away in the direction of Ursa Major, the Great Bear constellation.

Since its discovery 21 years ago, scientists have been looking for the companion star.

Observations at the W. M. Keck Observatory on Mauna Kea, Hawaii, suggested that the missing companion star radiated large amounts of ultraviolet (UV) light, but the area of the supernova was so crowded that scientists could not be sure they were measuring the right star.

The team combined optical light data and Hubble's UV light images to construct a spectrum that matched the predicted glow of a companion star, also known as the continuum emission. Scientists were only recently able to directly detect this light.

"We were able to get that UV spectrum with Hubble. This conclusively shows that you have an excess of continuum emission in the UV, even after the light from other stars has been subtracted," said Azalee Bostroem of the Space Telescope Science Institute (STScI) in Baltimore, Maryland.

Astronomers estimate a supernova occurs once every second somewhere in the universe, yet they don't fully understand how stars explode.

Further research will help astronomers better understand the properties of this companion star and the different types of supernovae.

The results of this study were published in the July 20 issue of the Astrophysical Journal.

More Information: "UNCOVERING THE PUTATIVE B-STAR BINARY COMPANION OF THE SN 1993J PROGENITOR" Authors: Ori D. Fox, K. Azalee Bostroem et al. - 2014 ApJ 790 17 doi:10.1088/0004-637X/790/1/17

Hubble extends stellar tape measure 10 times farther into space

By applying a technique called spatial scanning to an age-old method for gauging distances called astronomical parallax, scientists now can use NASA’s Hubble Space Telescope to make precision distance measurements 10 times farther into our galaxy than previously possible. 

Credit: NASA /ESA, A.Feild /STScI

Using NASA’s Hubble Space Telescope, astronomers now can precisely measure the distance of stars up to 10,000 light-years away—10 times farther than previously possible.

Astronomers have developed yet another novel way to use the 24-year-old space telescope by employing a technique called spatial scanning, which dramatically improves Hubble's accuracy for making angular measurements.

The technique, when applied to the age-old method for gauging distances called astronomical parallax, extends Hubble's tape measure 10 times farther into space.

"This new capability is expected to yield new insight into the nature of dark energy, a mysterious component of space that is pushing the universe apart at an ever-faster rate," said Noble laureate Adam Riess of the Space Telescope Science Institute (STScI) in Baltimore, Md.

Parallax, a trigonometric technique, is the most reliable method for making astronomical distance measurements, and a practice long employed by land surveyors here on Earth.

The diameter of Earth's orbit is the base of a triangle and the star is the apex where the triangle's sides meet.

The lengths of the sides are calculated by accurately measuring the three angles of the resulting triangle.

Astronomical Parallax works reliably well for stars within a few hundred light-years of Earth.

For example, measurements of the distance to Alpha Centauri, the star system closest to our sun, vary only by one arc second.

This variance in distance is equal to the apparent width of a dime seen from two miles away.

This illustration shows how the precision stellar distance measurements from NASA’s Hubble Space Telescope have been extended 10 times farther into our Milky Way galaxy than possible previously. 

This greatly extends the volume of space accessible to refining the cosmic yardstick needed for measuring the size of the universe. 

This most solid type of measurement is based on trigonometric Parallax, which is commonly used by surveyors. 

Because the stars are vastly farther away than a surveyor's sightline, Hubble must measure extremely small angles on the sky. 

Credit: NASA, ESA, and A. Feild (STScI)

Stars farther out have much smaller angles of apparent back-and-forth motion that are extremely difficult to measure.

Astronomers have pushed to extend the parallax yardstick ever deeper into our galaxy by measuring smaller angles more accurately.

This new long-range precision was proven when scientists successfully used Hubble to measure the distance of a special class of bright stars called Cepheid variables, approximately 7,500 light-years away in the northern constellation Auriga.

The technique worked so well, they are now using Hubble to measure the distances of other far-flung Cepheids.

Such measurements will be used to provide firmer footing for the so-called cosmic "distance ladder."

This ladder's "bottom rung" is built on measurements to Cepheid variables stars that, because of their known brightness, have been used for more than a century to gauge the size of the observable universe.

They are the first step in calibrating far more distant extra-galactic milepost markers such as Type Ia supernovae.

Riess and the Johns Hopkins University in Baltimore, Md., in collaboration with Stefano Casertano of STScI, developed a technique to use Hubble to make measurements as small as five-billionths of a degree.

To make a distance measurement, two exposures of the target Cepheid star were taken six months apart, when Earth was on opposite sides of the sun.

A very subtle shift in the star's position was measured to an accuracy of 1/1,000 the width of a single image pixel in Hubble's Wide Field Camera 3, which has 16.8 megapixels total.

A third exposure was taken after another six months to allow for the team to subtract the effects of the subtle space motion of stars, with additional exposures used to remove other sources of error.

NASA Kepler finds a very wobbly planet - Kepler-413b Binary System

This illustration shows the unusual orbit of planet Kepler-413b around a close pair of orange and red dwarf stars. 

The planet's 66-day orbit is tilted 2.5 degrees with respect to the plane of the binary star's orbit. 

The orbit of the planet wobbles around the central stars over 11 years, an effect called precession. 

This planet is also very unusual in that it can potentially precess wildly on its spin axis, much like a child's top. 

Credit: NASA, ESA, and A. Feild (STScI)

Imagine living on a planet with seasons so erratic you would hardly know whether to wear Bermuda shorts or a heavy overcoat.

That is the situation on a weird, wobbly world found by NASA's planet-hunting Kepler space telescope.

The planet, designated Kepler-413b, precesses, or wobbles, wildly on its spin axis, much like a child's top.

NASA's planet-hunting Kepler space telescope

The tilt of the planet's spin axis can vary by as much as 30 degrees over 11 years, leading to rapid and erratic changes in seasons.

In contrast, Earth's rotational precession is 23.5 degrees over 26,000 years.

Researchers are amazed that this far-off planet is precessing on a human timescale.

Precession : the axis of rotation of a precessing body itself rotates around another axis.

Kepler 413-b is located 2,300 light-years away in the constellation Cygnus. It circles a close pair of orange and red dwarf stars every 66 days.

Constellation Cygnus

The planet's orbit around the binary stars appears to wobble, too, because the plane of its orbit is tilted 2.5 degrees with respect to the plane of the star pair's orbit.

As seen from Earth, the wobbling orbit moves up and down continuously.

Kepler finds planets by noticing the dimming of a star or stars when a planet transits, or travels in front of them.

Normally, planets transit like clockwork. Astronomers using Kepler discovered the wobbling when they found an unusual pattern of transiting for Kepler-413b.

Veselin Kostov

"Looking at the Kepler data over the course of 1,500 days, we saw three transits in the first 180 days—one transit every 66 days—then we had 800 days with no transits at all. After that, we saw five more transits in a row," said Veselin Kostov, the principal investigator on the observation.

Kostov is affiliated with the Space Telescope Science Institute (STSCI) and Johns Hopkins University in Baltimore, Md.

The next transit visible from Earth's point of view is not predicted to occur until 2020.

This is because the orbit moves up and down, a result of the wobbling, in such a great degree that it sometimes does not transit the stars as viewed from Earth.

Astronomers are still trying to explain why this planet is out of alignment with its stars. There could be other planetary bodies in the system that tilted the orbit.

Or, it could be that a third star nearby that is a visual companion may actually be gravitationally bound to the system and exerting an influence.

Peter McCullough

"Presumably there are planets out there like this one that we're not seeing because we're in the unfavourable period," said Peter McCullough, a team member with the Space Telescope Science Institute (STSCI) and Johns Hopkins University.

"And that's one of the things that Veselin is researching: Is there a silent majority of things that we're not seeing?"

Even with its changing seasons, Kepler-413b is too warm for life as we know it.

Because it orbits so close to the stars, its temperatures are too high for liquid water to exist, making it inhabitable.

It also is a super Neptune—a giant gas planet with a mass about 65 times that of Earth—so there is no surface on which to stand.

StSci Team: 3D Printed Hubble Images for Blind Astronomers

Astronomers at the Space Telescope Science Institute (StSci) are experimenting with 3D printers to deliver Hubble imagery to the vision impaired. It is also useful as a learning tool for sighted people.

Credit: Space Telescope Science Institute

Hubble Image: RS Puppis puts on a spectacular light show

This Hubble image shows RS Puppis, a type of variable star known as a Cepheid variable. 

As variable stars go, Cepheids have comparatively long periods — RS Puppis, for example, varies in brightness by almost a factor of five every 40 or so days. 

Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA) - Hubble /Europe Collaboration Acknowledgment: H. Bond (STScI and Penn State University)

The NASA/ESA Hubble Space Telescope has observed the variable star RS Puppis over a period of five weeks, showing the star growing brighter and dimmer as it pulsates.

These pulsations have created a stunning example of a phenomenon known as a light echo, where light appears to reverberate through the murky environment around the star.

For most of its life, a star is pretty stable, slowly consuming the fuel at its core to keep it shining brightly.

However, once most of the hydrogen that stars use as fuel has been consumed, some stars evolve into very different beasts—pulsating stars.

They become unstable, expanding and shrinking over a number of days or weeks and growing brighter and dimmer as they do so.

A new and spectacular Hubble image shows RS Puppis, a type of variable star known as a Cepheid variable. As variable stars go, Cepheids have comparatively long periods.

RS Puppis, for example, varies in brightness by almost a factor of five every 40 or so days.

RS Puppis is unusual as it is shrouded by a nebula—thick, dark clouds of gas and dust.

Hubble observed this star and its murky environment over a period of five weeks in 2010, capturing snapshots at different stages in its cycle and enabling scientists to create a time-lapse video of this ethereal object.

The apparent motion shown in these Hubble observations is an example of a phenomenon known as a light echo. The dusty environment around RS Puppis enables this effect to be shown with stunning clarity.

As the star expands and brightens, we see some of the light after it is reflected from progressively more distant shells of dust and gas surrounding the star, creating the illusion of gas moving outwards.

This reflected light has further to travel, and so arrives at the Earth after light that travels straight from star to telescope.

This is analogous to sound bouncing off surrounding objects, causing the listener to hear an audible echo. In 2008, astronomers used the light echo around RS Puppis to measure its distance from us, obtaining the most accurate measurement of a Cepheid's distance.

While this effect is certainly striking in itself, there is another important scientific reason to observe Cepheids like RS Puppis.

The period of their pulsations is known to be directly connected to their intrinsic brightness, a property that allows astronomers to use them as cosmic distance markers.

This helps us to measure and understand the vast scale of the Universe.