The next big discovery in astronomy? Scientists probably found it years ago – but they don’t know it yet

An artist’s illustration of a black hole “eating” a star.
Credit: NASA/JPL-Caltech

Earlier this year, astronomers stumbled upon a fascinating
finding: Thousands
of black holes likely exist
near the center of our

The X-ray images that enabled this discovery weren’t from some
state-of-the-art new telescope
. Nor were they even recently
taken – some of the data was collected nearly 20 years ago.

No, the researchers discovered the black holes by digging
through old, long-archived data.

Discoveries like this will only become more common, as the era
of “big data” changes how science is done. Astronomers are
gathering an exponentially greater amount of data every day –
so much that it will take years to uncover all the hidden
signals buried in the archives.

The evolution of astronomy

Sixty years ago, the typical astronomer worked largely alone or
in a small team. They likely had access to a respectably large
ground-based optical telescope at their home institution.

Their observations were largely confined to optical wavelengths
– more or less what the eye can see. That meant they missed
signals from a host of astrophysical sources, which can emit
non-visible radiation from
very low-frequency radio all the way up to high-energy gamma
. For the most part, if you wanted to do astronomy, you
had to be an
academic or eccentric rich person
with access to a good

Old data was stored in the form of photographic plates or
published catalogs. But accessing archives from other
observatories could be difficult – and it was virtually
impossible for amateur astronomers.

The next big discovery in astronomy? Scientists probably found it years ago – but they don't know it yet
The Hubble Space Telescope. Credit: NASA

Today, there are observatories that cover the entire electromagnetic
. No longer operated by single institutions, these
state-of-the-art observatories are usually launched by space
agencies and are often
joint efforts involving many countries

With the coming of the digital age, almost all data are
publicly available shortly after they are obtained. This makes
astronomy very democratic – anyone who wants to can reanalyze
almost any data set that makes the news. (You too can look at
the Chandra data that led to the discovery of thousands of
black holes!)

These observatories generate a staggering amount of data. For
example, the Hubble Space Telescope, operating since 1990, has
made over 1.3
million observations
and transmits around 20 GB of raw data
every week, which is impressive for a telescope first designed
in the 1970s. The Atacama Large
Millimeter Array
in Chile now anticipates adding
2 TB of data
to its archives every day.

Data firehose

The archives of astronomical data are already impressively
large. But things are about to explode.

Each generation of observatories are usually at least
10 times more sensitive than the previous
, either because
of improved technology or because the mission is simply larger.
Depending on how long a new mission runs, it can detect
hundreds of times more astronomical sources than previous
missions at that wavelength.

For example, compare the early EGRET gamma ray observatory,
which flew in the 1990s, to NASA’s flagship mission Fermi,
which turns 10 this year. EGRET detected only about 190
gamma ray sources
in the sky. Fermi has seen over

The Large Synoptic Survey Telescope, an optical telescope

currently under construction in Chile
, will image the
entire sky every few nights. It will be so sensitive that it
will generate 10
million alerts per night
on new or transient sources,
leading to a catalog of over 15 petabytes after 10 years.

A black-hole-powered jet of hot gas in the giant elliptical
galaxy M87. Credit: NASA, ESA, E. Meyer, W. Sparks, J.
Biretta, J. Anderson, S.T. Sohn, and R. van der Marel
(STScI), C. Norman (Johns Hopkins University), and M.
Nakamura (Academia Sinica)

The Square Kilometre Array, when completed in 2020, will be the
most sensitive telescope in the world, capable of detecting
airport radar stations
of alien civilizations up to 50
light-years away. In just one year of activity, it will

generate more data than the entire internet

These ambitious projects will test scientists’ ability to
handle data. Images will need to be automatically processed –
meaning that the data will need to be reduced down to a
manageable size or transformed into a finished product. The new
observatories are pushing the envelope of computational power,
requiring facilities capable of processing hundreds of
terabytes per day

The resulting archives – all publicly searchable – will contain
1 million times more information that what can be stored on
your typical 1 TB backup disk.

Unlocking new science

The data deluge will make astronomy become a more collaborative
and open science than ever before. Thanks to internet archives,
learning communities
and new
outreach initiatives
, citizens can now participate in
science. For example, with the computer program Einstein@Home, anyone can use
their computer’s idle time to help search for gravitational
waves from colliding black holes.

It’s an exciting time for scientists, too. Astronomers like
myself often study physical phenomena on timescales so wildly
beyond the typical human lifetime that watching them in
real-time just isn’t going to happen. Events like a typical
galaxy merger –
which is exactly what it sounds like
– can take hundreds of
millions of years. All we can capture is a snapshot, like a
single still frame from a video of a car accident.

However, there are some phenomena that occur on shorter
timescales, taking just a few decades, years
or even seconds
. That’s how scientists discovered those
thousands of black holes in the new study. It’s also how they

recently realized
that the X-ray emission from the center
of a nearby dwarf galaxy has been fading since first detected
in the 1990s. These new discoveries suggest that more will be
found in archival spanning decades.

In my own work, I use Hubble archives to make movies of
high-speed plasma ejected in beams from . I used over 400 raw images spanning
13 years to make a movie of the
jet in nearby galaxy M87
. That movie showed, for the first
time, the twisting motions of the plasma, suggesting that the
jet has a helical structure.

This kind of work was only possible because other observers,
for other purposes, just happened to capture images of the
source I was interested in, back when I was in kindergarten. As
astronomical images become larger, higher resolution and ever
more sensitive, this kind of research will become the norm.

Explore further:

The largest catalog ever published of very high-energy gamma
ray sources in the Galaxy

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