Hubble Finds More Interesting Stuff

New data from the Spitzer and Hubble space telescopes show that in particular wavelengths of infrared light, some of the first galaxies to form in the Universe (less than 1 billion years after the Big Bang) were considerably brighter than astronomers anticipated.

No one yet knows for sure when the first stars in our Universe burst to life. Evidence suggests that between 100 million and 200 million years after the Big Bang, the Universe was filled mostly with neutral hydrogen gas that had perhaps just begun to coalesce into stars, which then began to form the first galaxies.

By about 1 billion years after the Big Bang, the Universe had become a sparkling firmament. Something else had changed, too: electrons of the omnipresent neutral hydrogen gas had been stripped away in a process known as ionization.

The Epoch of Reionization, the changeover from the Universe full of neutral hydrogen to one filled with ionized hydrogen, is well documented.

Before this Universe-wide transformation, long-wavelength forms of light, such as radio waves and visible light, traversed the Universe more or less unencumbered. But shorter wavelengths, including ultraviolet light, X-rays and gamma rays, were stopped short by neutral hydrogen atoms. These collisions would strip the neutral hydrogen atoms of their electrons, ionizing them.

But what could have produced enough ionizing radiation to affect all the hydrogen in the Universe? Was it individual stars? Giant galaxies?

If either were the culprit, those early cosmic colonizers would have been different than most modern stars and galaxies, which typically don’t release high amounts of ionizing radiation. Then again, perhaps something else entirely caused the event, such as quasars.

Researchers found that early galaxies were particularly bright in two specific wavelengths of infrared light produced by ionizing radiation interacting with hydrogen and oxygen gases within the galaxies. This implies that the galaxies were dominated by young, massive stars composed mostly of hydrogen and helium. They contain very small amounts of heavy elements, like nitrogen, carbon and oxygen, compared to stars found in modern galaxies.

These stars were not the first stars to form in the Universe (those would have been composed of hydrogen and helium only) but were still members of very early generations of stars.

The Epoch of Reionization wasn’t an instantaneous event, so while the new results are not enough to close the book on this cosmic event, they do provide new details about how the Universe evolved during this time and how the transition played out.

The findings are published in the Monthly Notices of the Royal Astronomical Society.

Sometimes the Abyss Stares Back

Astronomers have produced the largest, most comprehensive ‘history book’ of galaxies in the Universe, using 16 years’ worth of observations from the NASA/ESA Hubble Space Telescope. The endeavor is called the Hubble Legacy Field. The image, a combination of nearly 7,500 separate Hubble exposures, contains roughly 265,000 galaxies and stretch back through 13.3 billion years of time to just 500 million years after the Universe’s birth in the Big Bang.

Pictured: EVERYTHING

The Hubble Legacy Field combines observations taken by several Hubble deep-field surveys. In 1995, the Hubble Deep Field captured several thousand previously unseen galaxies. The subsequent Hubble Ultra Deep Field from 2004 revealed nearly 10,000 galaxies in a single image. The 2012 Hubble eXtreme Deep Field was assembled by combining ten years of Hubble observations taken of a patch of sky within the original Hubble Ultra Deep Field.

The new set of Hubble images, created from nearly 7,500 individual exposures, is the first in a series of Hubble Legacy Field images.

Happy Birthday Hubble

In celebration of the 29th anniversary of the launch of the NASA/ESA Hubble Space Telescope, astronomers captured this colorful look at the hourglass-shaped Southern Crab Nebula.

On April 24, 1990, Hubble was launched on the space shuttle Discovery. It has since revolutionized how astronomers and the general public see the Universe. The images it provides are spectacular from both a scientific and a purely aesthetic point of view.

Each year the telescope dedicates a small portion of its precious observing time to take a special anniversary image, focused on capturing particularly beautiful and meaningful objects. This year’s image is the Southern Crab Nebula, and it is no exception.

This incredible image of the Southern Crab Nebula was taken to mark Hubble’s 29th anniversary in space. Image credit: NASA / ESA / STScI.

The Southern Crab Nebula resides in the southern constellation Centaurus, approximately 7,000 light-years from Earth. It is so named to distinguish it from the better-known Crab Nebula, a supernova remnant visible in the constellation of Taurus.

The object appears to have two nested hourglass-shaped structures that were sculpted by a whirling pair of stars in a binary system. The duo consists of an aging red giant star and a white dwarf. The red giant is shedding its outer layers. Some of this ejected material is attracted by the gravity of the companion white dwarf.

The Southern Crab Nebula was assumed to be an ordinary star until 1989, when it was observed using telescopes at ESO’s La Silla Observatory.

The resulting image showed a roughly crab-shaped extended nebula, formed by symmetrical bubbles of gas and dust. Those observations only showed the outer hourglass emanating from a bright central region that could not be resolved.

It seems fitting that Hubble has returned to this object twenty years after its first observation. The new image adds to the story of an active and evolving object and contributes to the story of Hubble’s role in our evolving understanding of the Universe.

Passing Gas on Mars

Methane gas is periodically detected in the atmosphere of Mars. This was once considered implausible and perplexing, but it is now widely accepted by planetary scientists. Why the methane is there is still a mystery. It could point to present-day Martian microbes living in the rocks below the surface.

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Scientists working with the ESA’s Mars Express orbiter reported that in the summer of 2013, the spacecraft detected methane within Gale Crater, a 96-mile-wide depression near the Martian equator.

In the same summer of 2013, NASA’s Curiosity rover also measured a marked rise of methane in the air that lasted over two months.

The presence of methane is significant because the gas decays quickly. Calculations indicate that sunlight and chemical reactions in the thin Martian atmosphere would break up the molecules within a few hundred years, so any methane detected must have been created recently.

It could have been created by a geological process known as serpentinization, which requires both heat and liquid water. Or it could be a product of life, specifically methanogens, microbes that release methane as a waste product. Methanogens thrive in places lacking oxygen, such as rocks deep underground and the digestive tracts of animals.

Even if the source of the methane turns out to be geological, the hydrothermal systems that produce the emissions would still be prime locations to search for signs of life.

A newer European Mars spacecraft, the Trace Gas Orbiter, which has a more sophisticated methane detector, has been in orbit since 2017, but no results have been reported as of yet.

The Milky Way is Really Big

The Milky Way Galaxy (the one we’re in) contains an estimated 200 billion stars. But that’s just the tip of the iceberg, the Galaxy is surrounded by vast amounts of an unknown material called “dark matter” (matter that we can’t normally detect because it doesn’t interact with the electromagnetic spectrum). Astronomers know it exists because, dynamically, the Milky Way would fly apart if dark matter didn’t keep a gravitational lid on things.

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Still, astronomers would like to have a more precise measure of the Galaxy’s total mass to better understand how the myriad galaxies throughout the Universe form and evolve. A team of researchers from ESO, the Space Telescope Science Institute, the Johns Hopkins University Center for Astrophysical Sciences, and the University of Cambridge combined observations from the NASA/ESA Hubble Space Telescope and ESA’s Gaia satellite to study the motions of globular star clusters that orbit our Galaxy. The faster the clusters move under the entire Galaxy’s gravitational pull, the more massive it is. The team concluded the Milky Way has an equivalent mass of 1.54 trillion solar masses, most of it locked up in dark matter.

This new mass estimate puts the Milky Way Galaxy on the beefier side, compared to other galaxies in the Universe. The lightest galaxies are around a billion solar masses, while the heaviest are 30 trillion, or 30,000 times more massive. The Milky Way’s mass of 1.5 trillion solar masses is fairly normal for a galaxy of its brightness.

Previous estimates of the Milky Way’s mass ranged from 500 billion to 3 trillion solar masses. This huge margin of error arose primarily from the different methods used for measuring the distribution of dark matter, which makes up about 90% of the mass of the Galaxy.

Given the elusive nature of the dark matter, the team had to use a clever method to weigh the Milky Way, which relied on measuring the velocities of globular clusters, dense star clusters that orbit the spiral disk of the Galaxy at great distances.

The scientists used Gaia’s second data release, which includes measurements of globular clusters as far as 65,000 light-years from Earth, as a basis for the study.

Observations from Hubble allowed faint and distant globular clusters, as far as 130,000 light-years from Earth, to be added to the study. As Hubble has been observing some of these objects for a decade, it was possible to accurately track the velocities of these clusters as well.

By combining Gaia’s measurements with measurements from Hubble, the scientists could better pin down the Milky Way’s mass in a way that would be impossible without both space telescopes,

The team’s results will be published in the Astrophysical Journal.