Astronomers often describe Andromeda as a “sister galaxy” to our own Milky Way. It is relatively nearby, similarly sized, and comparably shaped. So what does it mean when we confirm that Andromeda is host to a “black hole bonanza”?

A black hole is born when a massive star collapses, resulting in a high concentration of gravity, so strong that light cannot even escape its pull. By definition, we can’t observe black holes directly, but astronomers can detect them if a close-orbiting star is pulled inside. Gravitational forces compress the star’s material, producing high-energy radiation in the process.

NASA’s Chandra X-ray observatory followed the radiation trail to identify 26 new black hole candidates, the largest number found outside of the Milky Way to date. Follow-up observations by the European Space Agency’s XMM-Newton X-ray observatory gave information useful for determining the nature of these black holes.

The first step in classifying Chandra’s findings: confirm the black hole sizes and locations. The process relies on perspective. In the same way a tall person standing far away can appear the same size as a short person much closer, objects in space can deceive us with their apparent size, so we need to look for additional clues. In the case of black holes, researchers saw bright and fast variability of X-ray emission to determine these 26 black holes are smaller “stellar mass” systems within Andromeda rather than supermassive black holes behind Andromeda.

As it turns out, neutron stars can look a lot like black holes from a distance, so researchers analyzed x-ray brightness and color. Neutron stars also emit x-ray radiation, but a black hole appears brighter—and a different color.

Eight of the black holes reside in globular clusters, concentrations of stars spherically distributed about the center of a galaxy that exist in both the Milky Way and Andromeda. However, astronomers have not yet discovered black holes in any of the Milky Way’s globular clusters.

“When it comes to finding black holes in the central region of a galaxy, it is indeed the case where bigger is better,” said co-author Stephen Murray of Johns Hopkins University and the Harvard-Smithsonian Center for Astrophysics (CfA). “In the case of Andromeda, we have a bigger bulge and a bigger supermassive black hole than in the Milky Way, so we expect more smaller black holes are made there as well.”

Perhaps the two galaxies aren’t as sisterly as we thought. The central bulge of Andromeda is larger, which explains why seven of the new candidates exist within 1,000 light years of Andromeda’s core.

Considering that we can only detect black holes when they are producing high-energy radiation, there must be more that we have not found yet—in both galaxies. Lead author Robin Barnard of CfA states, “While we are excited to find so many black holes in Andromeda, we think it’s just the tip of the iceberg, most black holes won’t have close companions and will be invisible to us.”

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image: NASA/JPL-Caltech/UCLA

I’m not going to get into exoplanet announcements such as this one or this one from yesterday morning’s meeting (as one attendee tweeted in summary, “There’s more exoplanets than you can shake an exostick at.”). We have ten press conferences scheduled, and three of them revolve around (pun intended) exoplanet discoveries. So I’ll plan for an exoplanet wrap-up toward the end of the conference.

Instead, I’d like to talk about the work of a few of those spiffy space-based telescopes—yes, the ever-popular Hubble Space Telescope, but also Chandra X-Ray Observatory and a new mission known as NuSTAR.

A grand effort known as the Hubble Ultra Deep Field (HUDF) has imaged the same, small, seemingly-dull part of the sky repeatedly at numerous, finely-tuned wavelengths of light, revealing distant galaxies that reside farther than just about anything we can see. Looking out into space means looking back into time, so the HUDF reveals an important epoch in the history of the Universe.

It turns out the Universe in its youth went through an unusual phase when most of the hydrogen in deep space was in the form of molecules, with no net electrical charge… By the time the Universe reached the age of about 800 million years, however, most of the hydrogen had become ionized, which is to say broken down into electrons and protons (both of which have electrical charge). But it takes energy to ionize hydrogen, so where did that energy come from?

This is the kind of puzzle that keeps astronomers busy (and employed) for decades. Since 2004, astronomers have refined and extended the HUDF observations to eke out more information about this epoch, and the most recent observations have allowed scientists to reach some well-founded, long-sought conclusions.

We know that young galaxies would emit radiation that could ionize the Universe, but can they produce enough radiation to light up the “Cosmic Dawn,” as it’s sometimes called? Astronomers love to come up with more exotic theories, such as the annihilation of dark matter, to explain things like this, but are such puzzling processes required?

Turns out they aren’t. Galaxies can do the job on their own. That’s not the sexiest answer, but it should ultimately feel quite satisfying: the Universe behaves in a way that we understand and can predict. But it took a remarkable amount of sleuthing to come up with this relatively mundane response.

First off, we tally up the galaxies we see, and we estimate how much radiation they would emit. And the first surprise? Small, faint (the researchers like to call ’em “feeble”) galaxies make a significant contribution to the total energy output, and the large, luminous can’t do the job on their own.

Turns out that the currently-observed population of galaxies does not produce enough radiation to ionize all that intergalactic hydrogen. Bummer. But we know that we’re not seeing all the galaxies! We can detect only the brightest ones at these great distances, and the HUDF team’s work suggests that an earlier generation of galaxies existed before the ones we’re seeing. So how can we estimate the energy contribution from what we’re not seeing directly?

The team of astronomers undertook the challenge of tallying the luminous galaxies versus the number of feeble galaxies, and projecting those estimates back in time. Based on HUDF and other observations from, for example, the Wilkinson Microwave Anisotropy Probe (WMAP), we can determine when stars and galaxies started lighting up the Universe, so when the team added up all the light from all the galaxies they estimated to have existed over that time… Bingo! Just enough light energy to ionize the Universe’s hydrogen.

All this work actually pushed Hubble to its limits. And it promises many more discoveries from the James Webb Space Telescope, due to launch in 2018, which will peer back farther in time to see earlier generations of galaxies.

Hubble isn’t alone out there, and x-ray astronomy in particular benefits from having telescopes in space. Stephen S. Murray from Johns Hopkins gave a review of “50 Years of X-Ray Astronomy,” describing remarkable successes in the field. From 1962 to 1999, x-ray astronomy has experienced an increase in sensitivity of 10 billion! (And Murray noted that it took astronomers 400 years to achieve that kind of gain in optical sensitivity…) That kind of revolutionary change has led to spectacular discoveries related to some of the most exotic objects in astronomy—including black holes, pulsars, and supernovae.

An impressive video from Chandra shows a curlicue jet streaming from the pulsar at the center of the Vela Supernova Remnant. This complex structure provides a nifty puzzle for astronomers to describe its origin.

And the recently-launched Nuclear Spectroscopic Telescope Array (NuSTAR), one of the least expensive missions ever launched by NASA, has released its first images. The pair of telescopes spotted two bright, energetic sources of x-rays in the galaxy IC 342—capturing black holes in the process of “feeding” (as NuSTAR team leader Fiona Harrison puts it).

Stay tuned for more spacy stuff the rest of the week…

NuSTAR image courtesy of CalTech

Upon further examination, astronomers realized that Swift had witnessed its brightest x-ray source since beginning operations in 2005 – a sudden flood of radiation that measured 5 times larger than the brightest burst previously observed and 14 times brighter than the brightest-known continuous source of x-rays in the sky.  According to Phil Evans, PhD, who authored parts of Swift’s software, “It was like trying to use a rain gauge and a bucket to measure the flow rate of a tsunami.”

The source, dubbed GRB 100621A, was a gamma ray burst, a sudden eruption of the highest-energy form of radiation known, followed by longer-lasting  “afterglows” of x-rays and other forms of energy. Originally discovered in 1967 by military satellites designed to detect secret nuclear weapons tests, gamma ray bursts originate in far outside the Milky Way Galaxy and are believed to occur as massive stars collapse to form black holes.

How much energy does such an event release?  Well, June’s record-breaking burst occurred nearly halfway across the observable universe!

Currently, astronomers detect gamma ray bursts roughly twice per day somewhere in the sky. Within a galaxy the size of the Milky Way, astronomers estimate that one gamma ray burst may occur about every 100,000 to 1,000,000 years.  Studies suggest that if one took place close enough to Earth – within, say, 3,000 light years – its radiation could have catastrophic effects on the planet’s biosphere.  No evidence suggests that this has happened in the past, but who knows what the future holds?  Of course, we have (smaller, but) bigger things to worry about closer to home…

Image: NASA/Swift/Stefan Immler

Published in the July 8 edition of the journal Nature, the finding is remarkable considering it was discovered by scientists who were looking at remnants from a supernova explosion.

Microquasars, as these objects are called, are not that uncommon. Universe Today points out that there are a dozen or so in our own Milky Way Galaxy. But the impressive size of this particular bubble, estimated at 1,000 light years across, makes it stand out from the crowd. Most microquasars in our own galaxy are less than 10 light years wide.

According to Universe Today, microquasars are formed by two objects—in this case, the small black hole and a companion star. Energy is produced

by matter falling from one component to the other, and can produce jets of high-speed particles. The fast jets slam into the surrounding interstellar gas, heating it and triggering an expanding bubble made of hot gas and ultra-fast particles colliding at different temperatures.

The jets seen in this microquasar are surprising and may alter the idea of how energy is emitted by a black hole. As New Scientist reports:

These jets are much more powerful than expected for a black hole of this size, blowing bubbles that expand faster than the speed of sound. The finding suggests that more of the energy spent by a black hole goes into accelerating matter– rather than emitting x-rays– than previously supposed.

Data in the form of x-ray emissions were gathered from both the European Southern Observatory and the Chandra X-ray Observatory in the study. Giant bubble-blowing black holes like this microquasar may help scientists better understand differences between black holes of different sizes—including the ones that lurk at the centers of most galaxies like our own.