This video is sponsored by Magellan TV.
Welcome to Launch Pad.
I'm Christian Ready, your friendly neighborhood astronomer.
And in this video we're going to talk about the discovery of not one but two rare double
quasars that existed 10 billion years ago in two pairs of merging galaxies.
So holy double, double quasars, Batman!
Quasars are the ultraluminous cores of active galaxies.
They are powered by supermassive black holes feeding on infalling matter.
As the black holes feed, they unleash a tremendous amount of energy, so much that they can be
seen from across the universe.
As a result, we can study the evolution of galaxies as far back as less than a billion
years after The Big Bang.
Double quasars are particularly interesting because they allow us to trace the mergers
of active galaxies in the early universe.
But double quasars are also very rare.
Only one in 1000 quasars come in pairs.
They're so close together they can only be resolved by the most powerful telescopes.
However, time on those telescopes is a precious commodity.
It's hard to justify their use if you don't know which quasars are double.
But now a team of astronomers have come up with a novel approach using the Sloan Digital
Sky Survey Ieces Gaia satellite, the Hubble Space Telescope Gemini North, and the very
Long Baseline Array to discover not one but two double quasars in the early universe.
We're going to talk about how they did it an what this means for probing the early universe
in a moment.
But first I'd like to take a second to thank Magellan TV who are very kindly sponsoring
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Quasars are the most energetic objects in the universe with luminosity's that are measured
in the trillions of Suns, and yet they're just about the size of the solar system.
They're so compact they appear as point sources.
In other words, they are indistinguishable from stars.
In fact, the name "quasar" is a shorthand for their official designation as "quasi-stellar
objects".
So how do we know that a point of light on the sky really is a quasar and not just some
run of the mill star in our Galaxy?
Well, there are two ways we can tell, both of which are found in the quasar's spectrum.
Ordinary stars feature absorption lines in their spectra that are caused by atoms in
their atmospheres absorbing light at specific wavelengths.
But quasars are trillions of times hotter than stars, so their spectra show powerful
emission lines.
And this is because the surrounding matter is so energized it radiates, adding extra
light to the quasar spectrum.
The second giveaway is that quasar spectra are shifted to longer, and therefore redder
wavelengths.
We call it "redshift".
As the universe expands, distant galaxies appear to be moving away from us faster than
nearby galaxies.
The faster the velocity, the greater its redshift.
Quasars are so distant and moving away from us so fast that spectral features that normally
would appear in the ultraviolet are shifted into the visible, and in some cases, to the
infrared parts of the spectrum.
So the greater the redshift, the farther away they are, and therefore the farther back in
time we are seeing them.
Most quasars appear at redshifts less than 2, which corresponds to roughly 9 billion
years ago.
But relatively few quasars have been found at higher redshifts, so finding double quasars
at higher redshift is especially desirable because there a way to study how active galaxies
merged in the early universe.
But so far, double quasars amount to just one-tenth of 1% of the thousands of quasars
known.
So how can we find these needles in the cosmic haystack?
Well, luckily a quasar's brightness varies overtime because the rate at which their supermassive
black holes feed can vary.
That causes a quasar to temporarily flare up over a few days to several weeks.
This gave a team of astronomers led by Yue Shen a clever idea.
A quasar pair would be separated by less than one arcsecond in the sky, and that's much
too close together to be resolved without a powerful telescope.
But each quasar in the pair feeds an brightens independently of the other, creating random
flare ups on other side of what otherwise would appear to be a bright star.
That would make the quasar appear to jitter on the sky by a very tiny amount, just 1/100th
of an arcsecond.
Now that's too small to be noticed by most telescopes, but it's a piece of cake for the
Gaia satellite to detect.
Gaia measures the tiny motions of stars as they move about the Galaxy.
As a matter of fact, Gaia uses quasars as a stationary background against which stars
motions can be measured.
But before searching through the Gaia catalog for jittering quasars, the team needed to
know which quasars were at a redshift greater than 2.
Since 2000, the Sloan Digital Sky Survey has built up a detailed 3 dimensional map of the
sky.
Its data set includes thousands of quasars and their redshifts.
The team selected quasars with redshifts greater than two, yet would still be bright enough
for Gaia to detect.
They found that Gaia detected tiny jitters in 15 of these quasars.
If these really were double quasars, the Hubble Space Telescope would be able to resolve them.
They submitted the 15 candidate quasars for a Hubble snapshot program.
Snapshots are a way to fill gaps in Hubble's observing schedule.
If the target can be imaged quickly, a snapshot is taken, and this keeps Hubble a productive
and respected member of society.
Of the 15 targets submitted, four were randomly observed.
The Quasar J1326 ended up being just a single object.
The jitter Gaia detected was probably just noise, which happens sometimes.
J0905 is clearly resolved into two objects, but they have different brightnesses and colors.
It turns out that the faint red object is a foreground red dwarf star, J0479 and J0841
both appear as a pair of point like cores that are similar in brightness and color to
each other.
That makes them strong candidates for double quasars, but the team needed to confirm that
both objects in each pair really were quasars and not just some chance alignment with a
bright foreground star.
To that end, they were granted observing time on the 8 meter Gemini North Telescope atop
Mauna Kea, Hawaii.
But this wasn't an ordinary observation for Gemini.
While splitting the quasar pairs a no brainer for Hubble.
It's a very tricky one for Gemini.
You see, even though Gemini has more than eleven times the light gathering area as Hubble,
it's still inside of Earth's atmosphere, so using Gemini to resolve the quasar pair would
push the telescope to its limit.
As a result, the team was granted some discretionary time for their observation.
Discretionary time is a small portion of observing time that's reserved for responding to unexpected
astronomical events, but it could also be used for high risk, high reward observations
such as the ones in this discovery.
On May 21st, 2020, the sky was exceptionally clear, and the air remarkably still on the
summit of Mauna Kea.
Under these pristine observing conditions, Gemini resolved the cores of
quasar J0841 and got Spectra of each core.
Both spectra had a very similar appearance and nearly identical redshifts.
There was no question that Gemini saw two quasars next to each other in the sky that
nigh.t based on the width of their emission lines, the team estimates the quasars had
masses of 2.5 billion and four billion Suns.
Unfortunately, the ideal observing conditions needed at Gemini didn't manifest themselves
again for the other quasar, so spectra couldn't be obtained for J0749.
But the team had one more trick up their sleeves.
Quasars are strong radio sources, while stars...not so much.
The team would need a radio telescope capable of resolving the quasar pair to verify that
each object was in fact a strong radio source.
But doing that would require linking several telescopes together to form a gigantic virtual
telescope.
Luckily, we just happen to have one called the Very Long Baseline Array.
VLBA is a series of 25 meter radio telescopes stretching from Mauna Kea, Hawaii to Saint
Croix in the US Virgin Islands.
When linked together, the array acts like a telescope with an 8611 kilometer aperture.
That's large enough to achieve a resolution 100 times sharper than Hubble.
Sure enough, VLBA detected each core of J0749 in the radio band of the spectrum.
Gemini and VLBA confirmed that Hubble's observations of J0841 and J0749 were in fact pairs of quasars.
However, there is one question left that hasn't been conclusively answered.
What if, either of the pairs was actually just one quasar that was being gravitationally
lensed by a foreground object, such as a faint galaxy?
Well, the Hubble observations didn't show any evidence of objects in front of the quasars,
but that doesn't necessarily rule out that there really isn't something there.
It's just that Hubble was a snapshot program and snapshots need to be relatively short
exposures.
Between Hubble's non-detection and the Gemini spectra, the team estimates that there is
a 27% chance that J0841 is in fact a lensed quasar.
The question would then need to be settled by deep infrared imaging of the pair to see
if there really are any foreground objects.
Perhaps this is something the James Webb Space Telescope can look into someday.
But for now, it's more likely that at least one, if not two of the four targets observed
by Hubble are in fact double quasars, and both with redshifts greater than two.
That would mean that we're seeing these pairs as they appeared around 10 billion years ago.
That's farther back in time than any double quasar found previously.
It's possible that we'll find more of these close pair quasars at higher redshift, because
the rate at which galaxies merged was much higher in the early universe.
Now that we have an effective technique for finding quasar pairs, this hypothesis can
be tested.
Even though galaxy mergers peaked billions of years ago, there is still very much a thing
in the universe today.
For example, NGC 6240 is a relatively nearby merger of galaxies.
Its central knotted region is believed to hold two and possibly even three supermassive
black holes.
The colliding galaxies look nothing like their former selves.
Tidal disruptions distorted their shapes and unleashed a barrage of star formation.
An even closer galactic merger will occur in the next few billion years.
The Milky Way is on a collision course with the Andromeda Galaxy.
As they collide their stars and gas will likely feed the supermassive black holes in their
merging cores and may even reignite them as quasars.
It'll be quite a sight to behold, but knowing our luck one of the quasar jets will be pointed
towards us an sterilize everything in its path.
Oh well.
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