good afternoon welcome to Goddard Space
Flight Center and todays space astronomy
update where we will have today some of
the most dramatic pictures yet from the
Hubble Space Telescope and here to tell
us about it and the findings is our
distinguished panel and our host Steve
marant an astronomer from Goddard Space
Flight Center Steve thanks Don and
welcome to space astronomy update
everybody originating today from Goddard
Space Flight Center in Greenbelt
Maryland and with us today to discuss
the birth pangs of stars like the Sun
and its solar system are three experts
have been investigating these objects
with the Hubble Space Telescope
professor Jeff Hester from the arizona
state university in tempe an
investigator of nebulae of some
distinction and a member of the original
wide field and planetary camera team for
the Hubble Space Telescope and also
we're glad to have a young postdoctoral
researcher dr. John Morse of the Space
Telescope Science Institute in Baltimore
did his PhD on these objects at
University of North Carolina a Harvard
graduate and welcome back to space
astronomy update one of the optics
experts of the Hubble Space Telescope a
member of the wide field and planetary
camera 2 team from the European Space
Agency in Space Telescope Science
Institute Chris burrows dr. Chris
burrows and our independent panelist
chairman of the department of astronomy
University of Washington in Seattle dr.
Bruce margon who is the chairman of the
board of the Astrophysical research
consortium and just appointed as the
next chairman of the board of the
Association of universities for research
in astronomy head of two boards but he
won't leave anyone bored because he's
one of the brilliant communicators of
the astronomical research now we're
talking about her big harrow objects and
Jeff Hester what are they and what have
you seen with the Hubble telescope well
I'll back up a little bit and first
start talking about why it is that star
formation is such a fascinating question
when we look at stars forming
astronomers never get a chance to
actually see stars for me but what we
can do instead is look out at different
objects and catch them
different stages in the formation
process and then use what we know with
physics and of our local environment to
put those together into a story which is
becoming a remarkably clean story
actually and this is exciting because
really what we're seeing here is what
happened five billion years ago when our
own son and our own solar system came
into being and so when we look at what
we're going to be looking at today it's
a bit of a time machine that lets us see
into our own history and some of the why
behind our own existence we could look
at the first graphic a very important
piece of this story was discovered in
the 1950s by two astronomers by the name
of George her big and Guillermo hello
and what they found were Jets of glowing
gas such as the jet here and the jet
here clumps of glowing gas rather moving
rapidly through space but we now
understand is happening is that right
about where the cross is now there's a
brand new star that's forming material
is flowing away from that star in two
Jet's one in this direction and one in
this direction it's called a bipolar
outflow that material is streaming away
from that forming star and then up in
this area and down in this area it's
running into ambient material the
material that was around that star this
is a Space Telescope picture of an
object called h81 to which is one of
four different objects that we're going
to see images of today a nice thing
about what we're going to see today
we're going to see images of four
separate objects and yet the story
that's being told in those four separate
objects is a common story you put it all
together and you start to get a clear
picture that answers some fundamental
questions about how it is that stars
form for example we're going to see some
data that shows us the immediate
environment around a forming star the
things that might lead to solar systems
and such as that we're going to see new
information that tells us about the
material flowing away from those stars
and in particular tells us that that
material brings with it the history of
what was happening with the star itself
and finally we're going to see a story
about how that material goes out and
interacts with the surroundings of the
star which might be an
piece of answering the question of what
makes stars the size that they are if I
could have the next graphic this is an
object called HH 34 and this is a
different object from the last one that
we showed you and what you see here
again is right down at about this
location right at the tip of that little
arrow shape is where the star itself is
the light that you see right around that
is light that's being reflected from the
cloud and the disk from which that star
is forming coming out away from that
star is an exceedingly thin jet and one
of the new results that will be talking
about today is the fact that that jet is
so very very thin right at its tip that
tells us it's coming from the star
itself almost that material then comes
streaming out through interstellar space
and if you see each of these knots along
here they sort of look like a train of
motorboats each of which has its own
little bow wave and that's a very
exciting new result when astronomers
first looked at these jets they
understood that they were clumpy but
many astronomers believe that those
clumps were in fact due to a smooth flow
in the jet that had some sort of funny
internal structure in it for those of
you who've watched a space shuttle take
off you might notice that there are
little diamond-shaped features behind
the shuttle main engines we now know
that's not what's going on in these jets
that in fact each one of these knots is
a separate little puff of material
bursts of material that came off of the
forming star and we can look at those
bursts and find out not only about the
jet itself but about the source finally
to to close up a few opening thoughts we
see jets in these forming stars but the
jets that we see in these forming stars
are also very similar to the jets that
astronomers see when they study
quasi-stellar objects when they study
radio galaxies when they study jets that
cover millions of light-years of
interstellar space and when they talk
about massive black holes at the Centers
of galaxies here we're looking at the
very same types of phenomena that now
close by where we can study them in more
d
Steve thank you Jeff Hester and John
Morris what have you seen of these
objects with bubble well aside from
investigating the origin of the Jets we
might also ask how these Jets interact
with their environments and how
important they an impact they may have
these new hubble space telescope images
show us for the first time the details
of the interactions between the Jets and
the interstellar gas first of all the
Jets travel at very high speeds hundreds
of kilometers per second and shockwaves
form along the flow where it interacts
with the interstellar gas causing the
jet and that interstellar gas to glow
the shockwaves sweep away material from
the protostar and may in fact restrict
how much material is available to build
the star secondly the Jets propagate for
very large distances at least several
yard light years in some cases they
deposit considerable energy into the gas
clouds which are forming stars and so
somewhat ironically if you have a gas
cloud which is sitting there forming
stars the actual process of star
formation may wind up destroying the gas
cloud for example let's look at the HH
47 system if we can bring up the first
graphic this is a ground-based image
taken by bo raipur at the european
southern observatory this is the outline
of the cloud here and there's a single
star which is forming down in the cloud
the star is located about right here
it's invisible in the optical but we can
detect it in the infrared this jet is
driving two Jet's one to the Northeast
which is up here which is slightly
inclined towards us so it comes out of
the cloud and we can see it the other
jet we can faintly see right here and it
is heading off in this direction
mawlid zoom in on the details that the
Hubble Space Telescope image shows us
first of all we see that the jet has
carved a hole in the gas cloud remember
the stars about right here and this jet
is speeding off to the northeast
direction here these white filaments are
the walls of the cavity and it's just
reflecting light from the star which is
here which is shining through the hole
carved out by the Jets the real news in
this story is that we can see these thin
shox structures along the edges of the
jet highlighted in blue green here
there's a series of them associated with
these knots and there's a big one up
here associated with the bow wave now
these thin structures had never been
seen before in exquisite detail that
we're seeing here and this is the first
time we've been able to tell how the jet
will transfer momentum to the gas cloud
okay Thank You Johnny Chris burrows you
were with us last when we discover these
or obtain a beautiful images of three
rings around supernova 1987a want to
know what you have to top it well in
some ways this desktop it what we see
with Hubble now is an image of star in
the closest star forming region so here
we have a unique opportunity this is the
closest star forming region to us and
we're looking at it with the most
powerful telescope available to humans
and what we see is is around the star we
see the disk of material that's falling
in to form the start and we see the jet
being formed this is the image that
we've obtained and you can see this disc
here this is the top surface of the disc
the back of the disc and this is the
front of the disc these are both being
lit up by the star that's forming in the
middle here now we can't see the star at
all because it's obscured behind the
disc itself it's there's a very dense
band of dust between us and the star and
in fact only one in a hundred billion
billion photons that come from that
star actually make it back out to us
directly but quite a few as you can see
a reflective from the disc so you can
see the shape of the disc and we're able
to quantitatively model it then we're
also able to see the jet as it comes out
from the star and it's as the disc
collapse on collapses to form the star
it's super heated and the jet is
material that's escaping and the only
free path perpendicular to the disk gets
jetted out in both directions and we're
able to see it as a very fine stream
coming right from the star it's
unresolved even by hubble clothes into
the star which means it's got the scales
of less than the size of our solar
system our solar system itself would fit
in this image at about that size there
across there so you can see that we're
seeing now on the scale of our own solar
system a star in the form in the process
of forming and indeed when this star has
formed the material that is left behind
in the disk could well eventually form
planets so okay Thank You Kris and Bruce
marg on these are amazing pictures of
jets and all I'm sure most people
haven't thought of phenomena like this
very much in there people read about how
the Sun might have formed it stars from
how does this fit with our solar system
good got into being well you're right
Steve that when people think about these
narrowly focused jets and astronomy they
normally think about a larger scale far
more violent events in astronomy like
quasi-stellar objects that are ejecting
huge amounts of material over scales and
millions of light years here we're
talking about a far more common
phenomenon indeed a phenomena every star
has to undergo namely collapsing from a
diffuse cloud to become a star and yet
we see that these Jets still occur and
they occur remarkably even though the
scale is far far smaller with the same
very very fine pointing in collimation
and perhaps most remarkably of all we
see these accretion disks these
flattened pancakes of gas that expel
these Jets now the most remarkable thing
that I've seen thus far is this very
most recent image that Christian shows
maybe we could put it back up
and if I were asked to draw on a napkin
for a student a disk of gas that is
falling on to something and some jets
that were then expelled out this is
exactly the drawing that I would make
but this is not a drawing this is a
picture this is an image obtained by the
Hubble Space Telescope of an accretion
disk accretion is a fundamental property
in astronomy the water can't fall right
down the bathtub drain the water has to
swirl around first no matter what the
environment in astronomy is the gas
can't fall right on to something that's
to swirl around for us to shed its spin
times to shut its angular momentum so
everyone is always said these disks must
form and you draw this little cartoon
but here we actually have an image of it
this is really in my mind the picture
that's worth a thousand words because
this object is close enough that we can
actually photograph this accretion disk
did we not see a year or two ago from
Hubble and this very program some dark
disk in the galaxy NGC 4261 or there
have been when object or another there
have been previous Hubble images of
active galaxies like NGC 4261 and
another one is Messier 87 where the
image shows a large donate donut shape
structure of gas and dust but those are
not accretion disks those are sort of
the reservoirs of gas on a much larger
spatial scale waiting their turn to fall
in and in those external galaxies the
actual accretion disk is much much too
small to be seen because as both Chris
and Jeff have indicated we're talking
about structures about the size of our
solar system here this object is close
enough and Hubble's angular resolution
ability to take sharp images is fine
enough that we can actually see the
pancake itself not the worst 830 picture
is the first real picture of an
accretion is certainly the first one of
which I'm aware and so on the one hand
everyone has always predicted this but
on the other hand to actually be able to
see it and have it come out so simply
and such hey an imitation of the cartoon
that you would draw to me is really
remarkable right well I think we've got
to go back to Chris burrows and find out
some more tell us tell us more about
what
design and the center of these stars
information well the these images
actually were were first captured in
January of a fabulet last year and we
were so excited to see this object but
we had to come back to it with Hubble
and get a second image so one thing I'm
going to show you is is an image this is
actually the second image we've taken
and it's another version of the image
you just saw just displayed in a
different way and you can clearly see
here these knots of material coming out
from the star in the jet and again each
pixel in this image each little square
block that you see is about 14
astronomical units across so that the
our solar system's 80 astronomical units
across so our solar system fits right in
there so we're seeing the material that
might eventually form a planetary system
around this star and we're seeing the
jet as it comes out from this disk
directly for the first time and it's
also clear I guess that the jet
collimation that the thing that can find
the jet in this pencil beam really
doesn't have very much to do with the
shape of the disk as had been theorized
it this has to be something that's
happening much closer to the star than
than the disc itself this is much
narrower than the Thunder and the cavity
in the disk right and the little black
spots along the red jet are the
individual little lumps no that was
actually the red jet itself maybe we can
put the image up a moment the red the
jet the red spots you see a knot in the
jet that are propagating away from the
star and then you can see a hint here of
the of the jet on the other side so
these blobs we actually know are moving
the other direction perhaps to visualize
this in three dimensions with John
Christie at the Space Telescope
Institute Kyle snapple felt at JPL and
Alan Watson at lowell observatory I made
a simulation which I'd like to show
which illustrates in perhaps in three
dimensions and this is a full physical
model of what's going on what you see
here is a rotator is the whole system
rotating so you can see it from many
different angles and this is we've been
able to describe in three dimensions
what the distribution of material in the
disc looks like and you can see that the
model fits very nicely onto the data
that we've got so we're understanding
in detail what's happening in this in
the system we're understanding you know
what the density is a function of
position and then that will help us to
build models which will explain how
eventually you could build planets for
example okay well we've seen Jeff Hess
sir we've seen a at least four different
her big arrow objects to the uninitiated
like myself they all look their friend I
suspect we'll see some more before we're
done today there ain't commonality in
all of this is well that's that's really
one of the exciting things about these
data often in astronomy we go and look
at this object and say wow that's wild
and then we look at this object and say
wow that's wild but here we're looking
at a number of different objects and
we're getting the same common picture
out of all of them and tells us that
we're really seeing not special
circumstances but really we're seeing a
picture of how it is that stars form as
a way of seeing that Chris was just
showing you a model of what's going on
in HH 30 with the disc and such as that
and if we could have the next graphic
here this is exactly the same model the
Chris was showing you for HH 30 except
this model has been turned on in the
little bit and so if you look at this
model what you see now is you see the
jet coming out away from the start very
narrow at the end you then see what
appears to be kind of a conical
reflection nebula here that's the top of
the disk and then you don't see the jet
on the other side because on the other
side the jet is in fact hiding behind
the material on the disk when we look at
HH 34 which was the same object that we
looked at before we see a picture that
looks very much like this model we can
have that graphic please in HH 34 keep
the model that you just saw in mind and
look at what we have here down at one
end the star itself is at this location
and we see kind of a conical reflection
nebula which is exactly what we saw in
that model of HH 30 when we turned it on
end we then see the jet coming out again
very very thin right down at the tip and
expanding somewhat as it moves out
through interstellar space again just as
we saw in the model of HH 30 and finally
we see the difference between this model
in nature
30 is that there is no jet here on the
other side it's actually there it's just
that we can't see it because it's hiding
behind that very dense disk from which
the star itself is forming while this
picture is up the other thing that I'll
talk about that's common between these
observations is the picture that we're
getting of these knots again I mentioned
in my opening comments that many
astronomers thought for a long time that
just a smooth flow of material was
coming out from the star and that the
knots that they saw from the ground were
things that were kind of happening
inside that smooth flow of material here
though we clearly see for example here a
clump with its own little bow wave or
hear a clump with its own little bow
wave and if you look at all of the jets
that we see today you get that same
basic picture that these are bursts that
are happening that the star does
something and it spits out material and
so these bursts are not talking is
telling us something about you know some
esoteric piece of gas dynamics that
happens as Jets travel through
interstellar space instead it's telling
us that stars when they form for reasons
that are not entirely clear to us yet
stars when they form from the very inner
most part of that disc in the star
itself are episodic they do something
for a while and then they go burst and
they send out a burst of material and
understanding the physics of why that
happens is going to be something that
any successful model of star formation
is going to have to come to grips with
okay now thanks Jeff talking about these
moving knots I think Chris burrows you
have couple images that blink them for
us right well I was how you measured
their motion yeah I actually mentioned
we saw this intriguing object laughs
februari and we were determined to come
back and take a second look so the first
look that we got actually is on the
screen now and we could take a look at
it what you see here these arrows are
pointing to some knots in the jet that
we saw this was in January of 90 in
February of 94 and then we took another
image in January this year and this is
the image that we saw then and you can
see that the knots have moved
in fact if you blink backwards and
forwards between these two images you
can see the knots are moving and because
we know how long ago that far apart in
time the images were taken and how far
away this object is we can compute how
fast the jet is moving it turns out for
example that the top job not there which
is the one moving fastest is moving at
something like 300 miles a second which
is if you like a thousandth of the speed
of light so these are very energetic
outflows that we're seeing which is why
they're able to propagate for hundreds
of billions of miles so now it's not a
matter of some kind of indirect esoteric
a guess and how quickly these blobs are
coasting out you're actually just
watching the motion from month to month
a month and measuring it directly is
that right that that's right although
we've been able to do this on the ground
but it's always taken years and years
before you'd have to look so that you
could detect this motion from the ground
and that may take five or ten years now
we're able to just measure it directly
in the space of 12 months and that means
that we can follow individual block
blobs through the you know through the
the kinks in the Jets and see how they
behave during those during those changes
in direction one of the one of the
mysteries which was Jeff may come back
to is why there are these kinks in the
Jets what's causing them now we'll be
able to literally take a video of the of
these knots as they go through the kinks
and understand better whether the knots
always keep going in the same direction
or whether they deviate and follow along
the jet as it bends through space and
what would this why hasn't this been
done before what would this image look
like if you took it from a ground-based
telescope well from the ground you
simply the central the central disc that
you're seeing this yellow and the in the
image would be would be unresolved you'd
see a fuzzy blob but you wouldn't be
able to tell that it wasn't just a point
star and in the knots here remember this
is the closest example the knots here
from the ground will be very difficult
to resolve there are only a few tenths
of an arcsecond department so the whole
thing what Billy just look like one
fuzzy mushroom right you'd see that
there was a jet there but you wouldn't
be able to resolve easily the individual
components and unfortunate that the
nearest one has just the ideal
orientation to our view that it's in
profile we learnt there are a number of
stars in this star forming region we've
looked at this is easily the best
example I see
okay I think we want to look into the
physics a little and ask Jeff fester and
John Morse you know what do you think
makes these things come out at
methodically and and if you want to get
into the kinks tell us about that too
well the the physics is the right word
the you know one of the very most
exciting things about this is that we're
finally getting a close enough look at
what's going on that we can start doing
some physics for some years people have
been calculating models using computers
to do simulations of what should be
happening in these Jets and they've been
calculating these models and we all go
off to meetings and look at them and say
oh that's very pretty but then we've
been turning through our data and our
data been of such a quality that we just
couldn't do a real comparison between
what we were seeing in the models in
between what we were seeing in the real
universe have more detailed in the
picture Jerry had more details in the
pictures the exciting thing here is that
we're finally actually able to see the
real objects well enough to start doing
that comparison we have a simulation
here in fact this is a simulation that
was carried out by a gemstone is at the
University of Maryland and what he did
is calculate what happens when a jet a
pulse jet consisting of lots of little
bursts comes flying out into the
surrounding interstellar gas and what
you see here these individual if I could
have a cursor on please a little
motorboat the little motor boats exactly
these individual knots are the pulses
that are coming out from the source and
you see that as they move along each one
has its own little bow wave just like a
motor boat has its little bow wave which
is exactly the kind of structure that
we're seeing when we're looking at these
jets and so all you have to do it was
when we got these data it was really
exciting because we had seen these
models for the past several years and
when you first looked at the hubble
space telescope images of these jets it
was like saying WOW I've seen that
picture before except it wasn't a
picture of something in space really
instead it was a picture of somebody's
calculation of what should be in space
and that's the kind of thing that when
it happens for an astronomer it's really
very very exciting because it tells you
just almost instantly that there's
something that now you understand that
or you didn't another piece of that
model that you just saw was the
individual blobs of gas coming along and
running into the bow wave at the end so
this material was coming along and one
not hit smack and then the next not
caught up with it and smack over and
over again well when you look at another
object this is a HH one if I could have
the next graphic please another very
exciting thing was that we saw exactly
the same phenomena there this is another
Hubble Space toss this is another Hubble
Space Telescope image this is in fact a
blow-up of the first Hubble Space
Telescope image that I showed you and if
I could have the graphic in the and the
cursor again please what you're seeing
here is the jet is coming in from this
direction and it's smacking into the
interstellar gas right here and so these
individual pulses are coming in over and
over again wham wham wham and what we
saw here that was really fascinating is
that right up here at the very front of
this is the bow wave of one of those
pulses and then immediately behind it
coming right up on its wake is the bow
wave of another one of those pulses and
so not only are we getting to see the
detailed physics of the jet itself and
speculate about what that jet tells us
about the star and the star formation
we're also getting to look at the other
end of it and seeing the effects of
these individual pulses coming in and
one after the other running into the
clouds of interstellar gas that's around
this object so it's really very exciting
stuff John Morris what what causes those
pulses well I wouldn't know but there
are people who might have an idea out
there determining that a the jet comes
from a very narrow region close to the
star is a huge result in these
observations secondly determining that
the jet is intrinsically pulsed is
another huge result it means that wild
matter is what falling down in the star
there's some sort of episodic phenomenon
occurring
now what that phenomenon is is open to
debate there are objects such as dwarf
novae which people know our binary
systems which involve accretion disks
onto a white dwarf and these objects
which have accretion disk around them
actually go through unstable periods and
they have outburst and so matter might
build up and then it would release and
then for a time the matter would build
up again and release again so you might
get episodic ejections or outbursts with
a disk phenomenon now the other
interesting analogy with that object is
that those objects don't always have the
same size outbursts sometimes the
outbursts are big sometimes the
outbursts are small and we do see
evidence for that in these stellar Jets
that there are different sizes of
outbursts perhaps we might debate that a
little bit but that's what I think
another phenomenon we see is that all of
the Jets that we've imaged although
they're straight and narrow which and
how narrow they are is quite remarkable
all of the Jets show signs or some sort
of wiggling motion that they don't go
perfectly straight they tend to bend
around a little bit now if we can bring
up the HH 47 HST image we could actually
see global Telescope image that's right
the wiggling in this particular jet is
more exaggerated than the other ones we
saw to remind you again the star is
right here in the cloud and the jet is
moving off to the upper left there's a
wiggle here another one over here it's
hard to say whether the jet actually
bounces back and forth here or whether
we're just seeing emission on the
surface of the jet which is actually
moving along here but there are clearly
lots of Wiggles and curves in here when
people look at this image the first
thing they think of is like a corkscrew
it looks like the jet may actually
spirally the gas are there and we know
that's definitely not what's occurring
so this jet goes fast down the middle
and slow at the edges and we have curb
shock waves in the middle of the jet
well John couldn't it be what's going on
is that the nozzle that's ejecting the
jet is itself undergoing these gyrations
it's it's possible and immediately when
you think of precession or some sort of
motion of the source you have to bring
in a component especially when the axis
wobbles around you have to bring in
another another star into the picture it
is known that many of the sources of
these Jets are in fact binaries but
whether all of them are is open to
question yet one of the one of the
exciting things as we've been getting
ready for this presentation in the last
couple of days and we've been arguing
among ourselves what it means they're
all manner of models that you can come
up with unless one or two okay you look
for example if you look at the time
scales for these pulses they range
anywhere from a few years to a few tens
of years and that's the same kind of
time that it takes say for a large
planet to orbit around the star or the
kind of time that it takes for two stars
to orbit around each other but it's also
the kind of time that it takes say for
the sun's magnetic field to change
directions and we know that there's a
good chance that these disks or that
these disks and jets are strongly
magnetic and that that's a major part of
it lots of other speculation and again
we're not giving you answers today but
instead we're saying that there's lots
of neat stuff in here and before we
really say that we understand star
formation we're going to have to say
that we understand all these phenomena
that we're speculating about today I'd
like to interject first that actually we
do not have direct evidence that the
Jets are strongly magnetic we have in
fact no evidence that the Jets are
strongly magnetic we know we believe
some work I did on my thesis I made
estimates that there are at least some
moderate magnetic fields far out in the
Jets way far away from the star now
those magnetic fields might be much
larger near the star were the whole
structures are compressed okay but i
would say that proudly magnetic fields
as far as the dynamics of the Jets don't
have much to do with the real shape of
well but there's a there's a response to
that I'll get off pretty quickly there's
a response to that and that is that we
can see where the gas is there are two
basic models for how these Jets are
collimated one of those models is that
there are magnetic fields that force the
gas to flow along in that direction the
other model is to say that there's gas
around that contains the Jets and when
you look at these pictures for example
both the HH 34 and chris is HH 30
observations you see that there isn't
gas right around the Jets like that in
fact that you see things are pretty well
wide open and this jet comes screaming
right out of the middle of it and it's
hard for me to imagine how you're going
to do that without invoking some strong
role for magnetic field well I would say
the role of the magnetic fields might be
very important by those are all right
return to in another five years or so
there's going to be a new camera on the
Hubble telescope will get even better
pictures and maybe we'll hear more about
it before then but right now I want to
thank all the panelists and give this
back to our announcer Don Savage Thank
You Steven panelists will start taking
questions if we have any here at Goddard
up scheming please Kate wait for the
microphone so we can get you picked up
and a please state your name and
affiliation thank you what are to the
extent that it can be understood the
range of masses either of the jets or of
the proto stars that are forming if this
is truly a common phenomenon the
presumably of a range of masses that
you're dealing with here yes the the
protostars that we're all looking at
probably have masses similar to those of
our Sun or in fact may be much smaller
these are all low mass stars as the
range of stellar masses
the masses in the Jets are yes much less
but they're about 110 million of a solar
mass lost per year in one of these Jets
so in order to get an appreciable amount
of mass loss in one of these Jets the
Jets would have to be very old and like
millions of years but they really aren't
there maybe a hundred thousand years old
at the most so the masses are very tiny
now what fraction of the mass that's
ejected in the jet as a fraction of how
much is falling onto the star that still
not real clear we know it's at least
probably about ten percent but but maybe
higher could be more and could explain
why why you don't make much way you
don't make massive stories you only make
low mass stars this way in fact I think
one of the most interesting things about
these pictures is for years guided only
by the extra galactic cases the flashy
exploding galaxies that have jets
astronomers are how are these jets made
the details look so complicated and all
that now I think we're beginning to
realize that the answer is why doesn't
everything have a jet that is it seems
like that this the process of accretion
is almost inevitably accompanied by the
process of this narrow collimated
expulsion the question is not how do you
make Jetts it seems to be any the
question is how do you avoid making Jets
because here we look at the very closest
cases of accretion that we can see
anywhere in the universe named we think
that are happening quite close to the
Sun and we see these things that we used
to think we're very exotic these over
here at the birth of the Sun Bruce you
would have seen an amazing fire rocket
going up I i think the conclusion is
becoming inescapable that you don't get
accretion disks without also getting
these narrow ejected fire hoses on all
different spatial scales whether they
are calm quiet formations of low-mass
stars or whether there are these very
violent accretion onto mass of nuclei of
entire galaxies though even these events
are not that common quiet given that the
materials blasted off this as ionized
plasma at hundreds of kilometers a
second so we're talking a very energetic
thing which is far more energy
thick than the star is when it's finally
been formed I wouldn't want to be
standing in the way any further
questions here at Goddard okay thank you
understand that there are no questions
from the other centers thank you for
joining us today and thank you panelist
Steve that concludes our program for
today
you